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1.  Proliferating cell nuclear antigen (PCNA): a key factor in DNA replication and cell cycle regulation 
Annals of Botany  2010;107(7):1127-1140.
Background
PCNA (proliferating cell nuclear antigen) has been found in the nuclei of yeast, plant and animal cells that undergo cell division, suggesting a function in cell cycle regulation and/or DNA replication. It subsequently became clear that PCNA also played a role in other processes involving the cell genome.
Scope
This review discusses eukaryotic PCNA, with an emphasis on plant PCNA, in terms of the protein structure and its biochemical properties as well as gene structure, organization, expression and function. PCNA exerts a tripartite function by operating as (1) a sliding clamp during DNA synthesis, (2) a polymerase switch factor and (3) a recruitment factor. Most of its functions are mediated by its interactions with various proteins involved in DNA synthesis, repair and recombination as well as in regulation of the cell cycle and chromatid cohesion. Moreover, post-translational modifications of PCNA play a key role in regulation of its functions. Finally, a phylogenetic comparison of PCNA genes suggests that the multi-functionality observed in most species is a product of evolution.
Conclusions
Most plant PCNAs exhibit features similar to those found for PCNAs of other eukaryotes. Similarities include: (1) a trimeric ring structure of the PCNA sliding clamp, (2) the involvement of PCNA in DNA replication and repair, (3) the ability to stimulate the activity of DNA polymerase ╬┤ and (4) the ability to interact with p21, a regulator of the cell cycle. However, many plant genomes seem to contain the second, probably functional, copy of the PCNA gene, in contrast to PCNA pseudogenes that are found in mammalian genomes.
doi:10.1093/aob/mcq243
PMCID: PMC3091797  PMID: 21169293
Proliferating cell nuclear antigen; PCNA; cyclin; DNA replication; DNA repair; cell cycle
2.  Identification and functional analysis of PCNA1 and PCNA-like1 genes of Phaseolus coccineus 
Journal of Experimental Botany  2009;61(3):873-888.
Proliferating cell nuclear antigen (PCNA) is an essential factor in DNA replication and in many other processes in eukaryotic cells. Genetic analysis of Phaseolus coccineus showed the presence of at least two PCNA-like genes in the runner bean genome. Two PCNA genes have previously been found in a few plant species including Arabidopsis, tobacco, and maize. In these species, genes were nearly identical. Two cDNAs of P. coccineus PCNA (PcPCNA1 and PcPCNA-like1) have been identified that differ distinctly from each other. Interestingly, both the genetic organization of PcPCNA1 and PcPCNA-like1 genes and their expression patterns were similar, but these were the only similarities between these genes and their products. The identity between PcPCNA1 and PcPCNA-like1 at the amino acid level was only 54%, with PcPCNA-like1 lacking motifs that are crucial for the activity typical of PCNA. Consequently, these two proteins showed different properties. PcPCNA1 behaved like a typical PCNA protein: it formed a homotrimer and stimulated the activity of human DNA polymerase delta. In addition, PcPCNA1 interacted with a p21 peptide and was recognized by an anti-human PCNA monoclonal antibody PC10. By contrast, PcPCNA-like1 was detected as a monomer and was unable to stimulate the DNA polymerase delta activity. PcPCNA-like1 also could not interact with p21 and was not recognized by the PC10 antibody. Our results suggest that PcPCNA-like1 either is unable to function alone and therefore might be a component of the heterotrimeric PCNA ring or may have other, yet unknown functions. Alternatively, the PcPCNA-like1 gene may represent a pseudogene.
doi:10.1093/jxb/erp354
PMCID: PMC2814116  PMID: 20007687
DNA polymerase delta; PCNA; Phaseolus coccineus; PRINS; RACE
3.  Plant Enzymes but Not Agrobacterium VirD2 Mediate T-DNA Ligation In Vitro 
Molecular and Cellular Biology  2000;20(17):6317-6322.
Agrobacterium tumefaciens, a gram-negative soil bacterium, transfers DNA to many plant species. In the plant cell, the transferred DNA (T-DNA) is integrated into the genome. An in vitro ligation-integration assay has been designed to investigate the mechanism of T-DNA ligation and the factors involved in this process. The VirD2 protein, which is produced in Agrobacterium and is covalently attached to T-DNA, did not, under our assay conditions, ligate T-DNA to a model target sequence in vitro. We tested whether plant extracts could ligate T-DNA to target oligonucleotides in our test system. The in vitro ligation-integration reaction did indeed take place in the presence of plant extracts. This reaction was inhibited by dTTP, indicating involvement of a plant DNA ligase. We found that prokaryotic DNA ligases could substitute for plant extracts in this reaction. Ligation of the VirD2-bound oligonucleotide to the target sequence mediated by T4 DNA ligase was less efficient than ligation of a free oligonucleotide to the target. T-DNA ligation mediated by a plant enzyme(s) or T4 DNA ligase requires ATP.
PMCID: PMC86106  PMID: 10938108

Results 1-3 (3)