Advances in the molecular characterisation of genetic muscle disease has been rapid, as demonstrated by a recent analysis of these conditions in the north of England by Norwood et al (2009), in which a genetic diagnosis was achieved for 75.7% of patients. However, there remain many patients with suspected genetic muscle disease in who a diagnosis is not obtained, often despite considerable diagnostic effort, and these patients are now being considered for the application of new technologies such as next generation sequencing. This study aimed to provide an in-depth phenotype analysis of undiagnosed patients referred to the Northern region muscle clinic with suspected genetic muscle disease, with the intention of gaining insight into these conditions, identifing cases with a shared phenotype who may be amenable to collective diagnostic testing or research, and evaluating the strengths and limitations of our current diagnostic strategy. We used two approaches: a review of clinical findings in patients with undiagnosed muscle disease, and a hierarchical cluster analysis to provide an unbiased interpretation of the phenotype data. These joint approaches identified a correlation of phenotypic features according to the age of disease onset and also delineated several interesting groups of patients, as well as highlighting areas of frequent diagnostic difficulty that could benefit from the use of new high-throughput diagnostic techniques.
Correspondence to: email@example.com
The formation and function of eukaryotic cilia/flagella require the action of a large array of dynein microtubule motor complexes. Due to genetic, biochemical, and microscopic tractability, Chlamydomonas reinhardtii has become the premier model system in which to dissect the role of dyneins in flagellar assembly, motility, and signaling. Currently, fifty-four proteins have been described as components of various Chlamydomonas flagellar dyneins or as factors required for their assembly in the cytoplasm and/or transport into the flagellum; orthologues of nearly all these components are present in other ciliated organisms including humans. For historical reasons, the nomenclature of these diverse dynein components and their corresponding genes, mutant alleles and orthologues has become extraordinarily confusing. Here, we unify Chlamydomonas dynein gene nomenclature and establish a systematic classification scheme based on structural properties of the encoded proteins. Furthermore, we provide detailed tabulations of the various mutant alleles and protein aliases that have been used and explicitly define the correspondence with orthologous components in other model organisms and humans.
Chlamydomonas; Cilia; Dynein; Flagella; Microtubule
There is little data on the impact of office-based buprenorphine therapy on criminal activity. The goal of this study was to determine the impact of primary care clinic-based buprenorphine maintenance therapy on rates of criminal charges and the factors associated with criminal charges in the 2 years after initiation of treatment.
We collected demographic and outcome data on 252 patients who were given at least one prescription for buprenorphine. We searched a public database of criminal charges and recorded criminal charges prior to and after enrollment. We compared the total number of criminal cases and drug cases 2 years before versus 2 years after initiation of treatment.
There was at least one criminal charge made against 38% of the subjects in the 2 years after initiation of treatment; these subjects were more likely to have used heroin, to have injected drugs, to have had any prior criminal charges, and recent criminal charges. There was no significant difference in the number of subjects with any criminal charge or a drug charge before and after initiation of treatment. Likewise, the mean number of all cases and drug cases was not significantly different between the two periods. However, among those who were opioid-negative for 6 or more months in the first year of treatment, there was a significant decline in criminal cases. On multivariable analysis, having recent criminal charges was significantly associated with criminal charges after initiation of treatment (adjusted odds ratio 3.92); subjects who were on opioid maintenance treatment prior to enrollment were significantly less likely to have subsequent criminal charges (adjusted odds ratio 0.52).
Among subjects with prior criminal charges, initiation of office-based buprenorphine treatment did not appear to have a significant impact on subsequent criminal charges.
Opioid-related disorders; Crime; Primary health care; Buprenorphine
To investigate pediatric chief residents' responsibilities and determine
how chief residents and program directors view the scope of the chief
We distributed a 20-item survey to program directors and chief residents at
all US pediatric residency programs. Questions pertained to activities
performed and the level of importance of administrative, clinical, and
educational activities. The survey also investigated motivating factors to
become chief resident, future career plans, and level of job
We received responses from 127 program directors and 101 chief residents. Of
the chief residents, 98% (99/101) felt administrative tasks were
very/somewhat important, followed by education, service, and research.
Significantly more program directors than chief residents felt chiefs'
overall workload was well balanced. Program directors gave higher ratings
than chief residents on chief's ability to develop clinical skills
(79% [95/121] versus 61% [61/100]) and
manage stress and burnout (86% [104/121] versus 72%
[72/100]). Future career plans for chief residents in decreasing
order included fellowship, outpatient practice, academic practice, and
working as a hospitalist. The most significant problems reported by the
chief residents were lack of administrative support and lack of time spent
in educational/clinical activities.
The chief resident role is primarily administrative, but program directors
and chiefs feel teaching and clinical responsibilities also are important.
Although the 2 groups agreed in many areas, program directors underestimated
the administrative demands placed on the chief residents, and our findings
suggest the chief resident role may be more fulfilling if the balance was
shifted somewhat toward teaching and clinical responsibilities.
Actin-dependent finger-like protrusions such as filopodia and microvilli are widespread in eukaryotes, but their assembly mechanisms are poorly understood. Filopodia assembly requires at least three biochemical activities on actin: actin filament nucleation, prolonged actin filament elongation, and actin filament bundling. These activities are shared by several mammalian formin proteins, including mDia2, FRL1 (also called FMNL1), and FRL2 (FMNL3). In this paper, we compare the abilities of constructs from these three formins to induce filopodia. FH1-FH2 constructs of both FRL2 and mDia2 stimulate potent filopodia assembly in multiple cell types, and enrich strongly at filopodia tips. In contrast, FRL1 FH1-FH2 lacks this activity, despite possessing similar biochemical activities and being highly homologous to FRL2. Chimeric FH1-FH2 experiments between FRL1 and FRL2 show that, while both an FH1 and an FH2 are needed, either FH1 domain supports filopodia assembly but only FRL2’s FH2 domain allows this activity. A mutation that compromises FRL2’s barbed end binding ability abolishes filopodia assembly. FRL2’s ability to stimulate filopodia assembly is not altered by additional domains (GBD, DID, DAD), but is significantly reduced in the full-length construct, suggesting that FRL2 is subject to inhibitory regulation. The data suggest that the FH2 domain of FRL2 possesses properties not shared by FRL1 that allow it to generate filopodia.
microvilli; FMNL3; mDia2; FH2 domain; bundling; FRL1
Endothelial cells form cell-cell adhesive structures, called adherens and tight junctions, which maintain tissue integrity, but must be dynamic for leukocyte transmigration during the inflammatory response and cellular remodeling during angiogenesis. This review will focus on Vascular Endothelial (VE)-cadherin, an endothelial-specific cell-cell adhesion protein of the adherens junction complex. VE-cadherin plays a key role in endothelial barrier function and angiogenesis, and consequently VE-cadherin availability and function are tightly regulated. VE-cadherin also participates directly and indirectly in intracellular signaling pathways that control cell dynamics and cell cycle progression. Here we highlight recent work that has advanced our understanding of multiple regulatory and signaling mechanisms that converge on VE-cadherin and have consequences for endothelial barrier function and angiogenic remodeling.
Equity focused health impact assessments (EFHIAs), or health equity impact assessments, are being increasingly promoted internationally as a mechanism for enhancing the consideration of health equity in the development of policies, programs and projects. Despite this there are relatively few examples of examples of completed EFHIAs available. This paper presents a case study of a rapid EFHIA that was conducted in Australia on a health promotion policy implementation plan. It briefly describes the process and findings of the EFHIA and evaluates the impact on decision-making and implementation.
The rapid EFHIA was undertaken in four days, drawing on an expert panel and limited review of the literature. A process evaluation was undertaken by email one month after the EFHIA was completed. An impact evaluation was undertaken two years later based on five semi-structured interviews with members of the EFHIA working group and policy officers and managers responsible for implementing the plan. A cost estimation was conducted by the EFHIA working group.
The EFHIA made both general and specific recommendations about how the health equity impacts of the policy implementation plan could be improved. The impact evaluation identified changes to development and implementation that occurred as a result of the EFHIA, though there was disagreement about the extent to which changes could be attributed solely to the EFHIA. Those responsible considered the recommendations of the EFHIA in the next versions of their ABHI implementation plans. Factors that influenced the impact of the EFHIA included consolidating understandings of equity, enabling discussion of alternatives, and differing understandings of the purpose of the EFHIA. The EFHIA cost US$4,036 to undertake.
This EFHIA was conducted in a short timeframe using relatively few resources. It had some reported impacts on the development of the implementation plan and enhanced overall consideration of health equity. This case highlights some of the factors and preconditions that may maximise the impact of future EFHIAs on decision-making and implementation.
Adenomatous polyposis coli is a cytoskeletal organizer and a scaffold for mediating degradation of the Wnt effector β-catenin. We uncouple these different APC functions and show that GSK3β/CKI phosphorylation regulates APC clusters and cell migration independently of cell–cell adhesion and β-catenin transcriptional activity.
Adenomatous polyposis coli (APC), a tumor suppressor commonly mutated in cancer, is a cytoskeletal organizer for cell migration and a scaffold for GSK3β/CKI-mediated phosphorylation and degradation of the Wnt effector β-catenin. It remains unclear whether these different APC functions are coupled, or independently regulated and localized. In primary endothelial cells, we show that GSK3β/CKI-phosphorylated APC localizes to microtubule-dependent clusters at the tips of membrane extensions. Loss of GSK3β/CKI-phosphorylated APC from these clusters correlates with a decrease in cell migration. GSK3β/CKI-phosphorylated APC and β-catenin at clusters is degraded rapidly by the proteasome, but inhibition of GSK3β/CKI does not increase β-catenin–mediated transcription. GSK3β/CKI-phosphorylated and -nonphosphorylated APC also localize along adherens junctions, which requires actin and cell–cell adhesion. Significantly, inhibition of cell–cell adhesion results in loss of lateral membrane APC and a concomitant increase in GSK3β/CKI-phosphorylated APC in clusters. These results uncouple different APC functions and show that GSK3β/CKI phosphorylation regulates APC clusters and cell migration independently of cell–cell adhesion and β-catenin transcriptional activity.
Chlamydomonas reinhardtii is a unicellular green alga whose lineage diverged from land plants over 1 billion years ago. It is a model system for studying chloroplast-based photosynthesis, as well as the structure, assembly, and function of eukaryotic flagella (cilia), which were inherited from the common ancestor of plants and animals, but lost in land plants. We sequenced the ∼120-megabase nuclear genome of Chlamydomonas and performed comparative phylogenomic analyses, identifying genes encoding uncharacterized proteins that are likely associated with the function and biogenesis of chloroplasts or eukaryotic flagella. Analyses of the Chlamydomonas genome advance our understanding of the ancestral eukaryotic cell, reveal previously unknown genes associated with photosynthetic and flagellar functions, and establish links between ciliopathy and the composition and function of flagella.
Chronic gastritis induced by Helicobacter pylori is the strongest known risk factor for gastric adenocarcinoma, yet the effects of bacterial eradication on carcinogenesis remain unclear. Animal models provide important insights into factors that are involved in gastric carcinogenesis, and we previously utilized such a model to demonstrate that an in vivo adapted H. pylori strain, 7.13, rapidly and reproducibly induces inflammation-mediated gastric carcinoma. In the current study, we used this bacterial strain as a prototype to define the role of targeted antimicrobial therapy in gastric carcinogenesis. Mongolian gerbils were infected with H. pylori for 4 or 8 weeks, treated with antimicrobial agents or vehicle, and then euthanized at 8 weeks after the completion of therapy. All infected gerbils developed gastritis; however, inflammation was significantly attenuated in animals receiving antimicrobial therapy. Gastric dysplasia or cancer developed in > 60% of the gerbils that remained persistently colonized with H. pylori, but in none of the animals treated with antibiotics following 4 weeks of infection. Infection with H. pylori for 8 weeks prior to therapy resulted in an attenuation, but not complete prevention, of pre-malignant and malignant lesions. Similarly, antibiotic therapy initiated at 4, but not 8, weeks after H. pylori challenge significantly reduced expression of the Th1 pro-inflammatory cytokine interferon-γ within colonized gastric mucosa. These results indicate that treatment of H. pylori in this model decreases the incidence and severity of lesions with carcinogenic potential. The effectiveness of eradication is dependent upon the timing of intervention, providing insights into mechanisms that may regulate the development of malignancies arising within the context of inflammatory states.
inflammation; cytokine; dysplasia; gastric cancer; antibiotics
Organic anion transporting polypeptide 1B3 (OATP1B3, SLCO1B3) is normally expressed in hepatocytes. In this study, we demonstrated frequent overexpression of OATP1B3 in colorectal adenocarcinomas. Quantitative RT-PCR analysis of 17 colon tumors indicated tumoral overexpression of OATP1B3 by ~100 fold, compared to 20 normal colon samples (p<0.0001). Using immunohistochemistry on a tissue microarray containing 93 evaluable colon tumor specimens, we detected immunostaining of OATP1B3 in 75 colon adenocarcinomas (81%) and no immunostaining in normal samples. To determine the functional effects of OATP1B3 expression on drug-induced apoptosis, we used camptothecin and oxaliplatin on a panel of colorectal cancer cell lines stably overexpressing OATP1B3. The results indicated that OATP1B3 overexpression enhanced cell survival in RKO, HCT-8 and HCT116p53+/+ cells that harbor wildtype p53 but not in Caco-2 and HCT116p53-/- cells that lack p53, compared to the respective empty vector controls (p<0.01). The TUNEL assay confirmed that HCT116p53+/+ cells overexpressing OATP1B3 had significantly lower apoptotic levels compared to empty vector control (P<0.001). The overexpression of OATP1B3 reduced the transcriptional activity of p53, with subsequent reductions in transcript and protein levels of its downstream transcription targets (P21WAF1 and PUMA). Overexpression of a point mutation (G583E) variant of OATP1B3 lacking transport activity did not confer an antiapoptotic effect or affect p53 transcriptional activity, suggesting that the antiapoptotic effect of OATP1B3 may be associated with its transport activity. Taken together, our results suggest that OATP1B3 overexpression in colorectal cancer cells may provide a survival advantage by altering p53-dependent pathways.
Residents of socioeconomically disadvantaged locations are more likely to have poor health than residents of socioeconomically advantaged locations and this has been comprehensively mapped in Australian cities. These inequalities present a challenge for the public health workers based in or responsible for improving the health of people living in disadvantaged localities. The purpose of this study was to develop a generic workforce needs assessment tool and to use it to identify the competencies needed by the public health workforce to work effectively in disadvantaged communities.
A two-step mixed method process was used to identify the workforce needs. In step 1 a generic workforce needs assessment tool was developed and applied in three NSW Area Health Services using focus groups, key stakeholder interviews and a staff survey. In step 2 the findings of this needs assessment process were mapped against the existing National Health Training Package (HLT07) competencies, gaps were identified, additional competencies described and modules of training developed to fill identified gaps.
There was a high level of agreement among the AHS staff on the nature of the problems to be addressed but less confidence indentifying the work to be done. Processes for needs assessments, community consultations and adapting mainstream programs to local needs were frequently mentioned as points of intervention. Recruiting and retaining experienced staff to work in these communities and ensuring their safety were major concerns. Workforce skill development needs were seen in two ways: higher order planning/epidemiological skills and more effective working relationships with communities and other sectors. Organisational barriers to effective practice were high levels of annual compulsory training, balancing state and national priorities with local needs and giving equal attention to the population groups that are easy to reach and to those that are difficult to engage. A number of additional competency areas were identified and three training modules developed.
The generic workforce needs assessment tool was easy to use and interpret. It appears that the public health workforce involved in this study has a high level of understanding of the relationship between the social determinants and health. However there is a skill gap in identifying and undertaking effective intervention.
Home visiting programs comprising intensive and sustained visits by professionals (usually nurses) over the first two years of life show promise in promoting child health and family functioning, and ameliorating disadvantage. Australian evidence of the effectiveness of sustained nurse home visiting in early childhood is limited. This paper describes the method and cohort characteristics of the first Australian study of sustained home visiting commencing antenatally and continuing to child-age two years for at-risk mothers in a disadvantaged community (the Miller Early Childhood Sustained Home-visiting trial).
Methods and design
Mothers reporting risks for poorer parenting outcomes residing in an area of socioeconomic disadvantage were recruited between February 2003 and March 2005. Mothers randomised to the intervention group received a standardised program of nurse home visiting. Interviews and observations covering child, maternal, family and environmental issues were undertaken with mothers antenatally and at 1, 12 and 24 months postpartum. Standardised tests of child development and maternal-child interaction were undertaken at 18 and 30 months postpartum. Information from hospital and community heath records was also obtained.
A total of 338 women were identified and invited to participate, and 208 were recruited to the study. Rates of active follow-up were 86% at 12 months, 74% at 24 months and 63% at 30 months postpartum. Participation in particular data points ranged from 66% at 1 month to 51% at 24 months postpartum. Rates of active follow-up and data point participation were not significantly different for the intervention or comparison group at any data point. Mothers who presented for antenatal care prior to 20 weeks pregnant, those with household income from full-time employment and those who reported being abused themselves as a child were more likely to be retained in the study. The Miller Early Childhood Sustained Home-visiting trial will provide Australian evidence of the effectiveness of sustained nurse home visiting for children at risk of poorer health and developmental outcomes.
Background and aims:
OATP1B3 is an organic anion transporting polypeptide (OATP) that functions as a multispecific transporter in the normal liver. We examined the expression and clinical significance of OATP1B3 in colon cancers in tissue microarrays.
Immunohistochemistry was used to assess OATP1B3 protein expression in paraffinized colon tumor tissue microarrays. OATP1B3 immunostaining was evaluated by location and intensity. Relationships between OATP1B3 expression, known prognostic variables and clinical outcomes were examined.
278 colon tumor samples of all stages were evaluated for OATP1B3 expression. OATP1B3 immunostaining was detectable in the majority (56%) of the tumor samples. Higher OATP1B3 expression was seen in lower stage tumors (p = 0.003) and lower grade (p = 0.004) tumors, but was not predictive of 5-year survival or tumor recurrence as an independent variable. Within individual tumor grades, OATP1B3 expression was associated with improved 5-year survival, but not recurrence in patients with poorly differentiated tumors.
OATP1B3 expression was seen in the majority of colon tumors and may be a marker of lower grade and lower stage tumors and may predict for improved outcome in certain tumors.
tissue array analysis; colon neoplasms; organic anion transporters; tumor markers; immunohistochemistry
As socioeconomic health inequalities persist and widen, the health effects of adversity are a constant presence in the daily work of physicians. Gruen and colleagues suggest that, in responding to important population health issues such as this, defining those areas of professional obligation in contrast to professional aspiration should be on the basis of evidence and feasibility. Drawing this line between obligation and aspiration is a part of the work of professional medical colleges and associations, and in doing so they must respond to members as well as a range of other interest groups. Our aim was to explore the usefulness of Gruen's model of physician responsibility in defining how professional medical colleges and associations should lead the profession in responding to socioeconomic health inequalities.
We report a case study of how the Royal Australian College of General Practitioners is responding to the issue of health inequalities through its work. We undertook a consultation (80 interviews with stakeholders internal and external to the College and two focus groups with general practitioners) and program and policy review of core programs of College interest and responsibility: general practitioner training and setting of practice standards, as well as its work in public advocacy.
Some strategies within each of these College program areas were seen as legitimate professional obligations in responding to socioeconomic health inequality. However, other strategies, while potentially professional obligations within Gruen's model, were nevertheless contested. The key difference between these lay in different moral orientations. Actions where agreement existed were based on an ethos of care and compassion. Actions that were contested were based on an ethos of justice and human rights.
Colleges and professional medical associations have a role in explicitly leading a debate about values, engaging both external stakeholder and practicing member constituencies. This is an important and necessary step in defining an agreed role for the profession in addressing health inequalities.
Clustering and assembly of expressed sequence tags (ESTs) constitute the basis for most genomewide descriptions of a transcriptome. This approach is limited by the decline in sequence quality toward the end of each EST, impacting both sequence clustering and assembly. Here, we exploit the available draft genome sequence of the unicellular green alga Chlamydomonas reinhardtii to guide clustering and to correct errors in the ESTs. We have grouped all available EST and cDNA sequences into 12 063 ACEGs (assembly of contiguous ESTs based on genome) and generated 15 857 contigs of average length 934 nt. We predict that roughly 3000 of our contigs represent full-length transcripts. Compared to previous assemblies, ACEGs show extended contig length, increased accuracy and a reduction in redundancy. Because our assembly protocol also uses ESTs with no corresponding genomic sequences, it provides sequence information for genes interrupted by sequence gaps. Detailed analysis of randomly sampled ACEGs reveals several hundred putative cases of alternative splicing, many overlapping transcription units and new genes not identified by gene prediction algorithms. Our protocol, although developed for and tailored to the C. reinhardtii dataset, can be exploited by any eukaryotic genome project for which both a draft genome sequence and ESTs are available.
In recent years, national and state/territory governments have undertaken an increasing number of initiatives to strengthen general practice and improve its links with the rest of the primary health care sector. This paper reviews how far these initiatives were contributing to a well functioning and comprehensive primary health care system during the period 2000–2002, using a normative model of primary health care and data from a descriptive study to evaluate progress.
There was a significant number of programs, at both state/territory and national level. Most focused on individual care, particularly for chronic disease, rather than population health approaches. There was little evidence of integration across programs: each tended to be based in and focus on a single jurisdiction, and build capacity chiefly within the services funded through that jurisdiction. As a result, the overall effect was patchy, with similar difficulties being noted across all jurisdictions and little gain in overall system capacity for effective primary health care.
Efforts to develop more effective primary health care need a more balanced approach to reform, with a better balance across the different elements of primary health care and greater integration across programs and jurisdictions. One way ahead is to form a single funding agency, as in the UK and New Zealand, and so remove the need to work across jurisdictions and manage their competing interests. A second, perhaps less politically challenging starting point, is to create an agreed framework for primary health care within which a collective vision for primary health care can be developed, based on population health needs, and the responsibilities of different sectors services can be negotiated. Either of these approaches would be assisted by a more systematic and comprehensive program of research and evaluation for primary health care.
The effects of socioeconomic position on health have been largely ignored in clinical guidelines. Australia's National Health and Medical Research Council has produced a framework to ensure that they are taken into account
Geobacter sulfurreducens contains a 9.6-kDa c-type cytochrome that was previously proposed to serve as an extracellular electron shuttle to insoluble Fe(III) oxides. However, when the cytochrome was added to washed-cell suspensions of G. sulfurreducens it did not enhance Fe(III) oxide reduction, whereas similar concentrations of the known electron shuttle, anthraquinone-2,6-disulfonate, greatly stimulated Fe(III) oxide reduction. Furthermore, analysis of the extracellular c-type cytochromes in cultures of G. sulfurreducens demonstrated that the dominant c-type cytochrome was not the 9.6-kDa cytochrome, but rather a 41-kDa cytochrome. These results and other considerations suggest that the 9.6-kDa cytochrome is not an important extracellular electron shuttle to Fe(III) oxides.
The dissimilatory Fe(III) reducer Geobacter metallireducens reduced Fe(III) bound in humic substances, but the concentrations of Fe(III) in a wide range of highly purified humic substances were too low to account for a significant portion of the electron-accepting capacities of the humic substances. Furthermore, once reduced, the iron in humic substances could not transfer electrons to Fe(III) oxide. These results suggest that other electron-accepting moieties in humic substances, such as quinones, are the important electron-accepting and shuttling agents under Fe(III)-reducing conditions.
To evaluate which microorganisms might be responsible for microbial reduction of humic substances in sedimentary environments, humic-reducing bacteria were isolated from a variety of sediment types. These included lake sediments, pristine and contaminated wetland sediments, and marine sediments. In each of the sediment types, all of the humic reducers recovered with acetate as the electron donor and the humic substance analog, 2,6-anthraquinone disulfonate (AQDS), as the electron acceptor were members of the family Geobacteraceae. This was true whether the AQDS-reducing bacteria were enriched prior to isolation on solid media or were recovered from the highest positive dilutions of sediments in liquid media. All of the isolates tested not only conserved energy to support growth from acetate oxidation coupled to AQDS reduction but also could oxidize acetate with highly purified soil humic acids as the sole electron acceptor. All of the isolates tested were also able to grow with Fe(III) serving as the sole electron acceptor. This is consistent with previous studies that have suggested that the capacity for Fe(III) reduction is a common feature of all members of the Geobacteraceae. These studies demonstrate that the potential for microbial humic substance reduction can be found in a wide variety of sediment types and suggest that Geobacteraceae species might be important humic-reducing organisms in sediments.
Chloroplast protein synthesis in Chlamydomonas reinhardtii is dispensable when cells are provided acetate as a carbon source. Mutants defective in synthesis, assembly, or function of chloroplast ribosomes are therefore conditionally viable. Positive selection of nonphotosynthetic cells on arsenate has been combined with a simple screening procedure to isolate mutants with a broad spectrum of defects in chloroplast protein synthesis. Eight new mutants deficient in chloroplast ribosomes have been isolated. Three of these have been characterized genetically and phenotypically, and compared with two previously described ribosome mutants, ac-20 and cr-1. A working model of ribosome assembly is proposed which suggests possible biochemical roles for these five Mendelian gene loci.