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1.  On the Origin of Cells and Viruses: Primordial Virus World Scenario 
It is proposed that the pre-cellular stage of biological evolution unraveled within networks of inorganic compartments that harbored a diverse mix of virus-like genetic elements. This stage of evolution might comprise the Last Universal Cellular Ancestor (LUCA) that more appropriately could be denoted Last Universal Cellular Ancestral State (LUCAS). This scenario for the origin of cellular life recapitulates the early ideas of J. B. S. Haldane sketched in his classic 1928 essay. However, unlike in Haldane’s day, there is now considerable support for this scenario from three major lines of comparative-genomic evidence: i) lack of homology between the core components of the DNA replication systems of the two primary lines of descent of cellular life forms, archaea and bacteria, ii) distinct membrane chemistries and lack of homology between the enzymes of lipid biosynthesis in archaea and bacteria, iii) spread of several viral hallmark genes, which encode proteins with key functions in viral replication and morphogenesis, among numerous and extremely diverse groups of viruses, in contrast to their absence in cellular life forms, iv) the extant archaeal and bacterial chromosomes appear to be shaped by accretion of diverse, smaller replicons, suggesting a continuity between the hypothetical, primordial virus stage of life’s evolution and the dynamic prokaryotic world that existed ever since. Under the viral model of pre-cellular evolution, the key components of cells including the replication apparatus, membranes, and molecular complexes involved in membrane transport and translocation originated as components of virus-like entities. The two surviving types of cellular life forms, archaea and bacteria, might have emerged from the LUCAS independently, along with, probably, numerous forms now extinct.
doi:10.1111/j.1749-6632.2009.04992.x
PMCID: PMC3380365  PMID: 19845627
comparative genomics; evolution of cells; evolution of viruses; origin of membranes; viral hallmark genes

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