On the origin of cells and viruses: primordial virus world scenario.

It is proposed that the precellular 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 makes up the Last Universal Cellular Ancestor (LUCA) that more appropriately could be denoted Last Universal Cellular Ancestral State (LUCAS). Such a scenario recapitulates the ideas of J. B. S. Haldane sketched in his classic 1928 essay. However, unlike in Haldane's day, considerable support for this scenario exits today: lack of homology between core DNA replication system components in archaea and bacteria, distinct membrane chemistries and enzymes of lipid biosynthesis in archaea and bacteria, spread of several viral hallmark genes among diverse groups of viruses, and the extant archaeal and bacterial chromosomes appear to be shaped by accretion of diverse, smaller replicons. Under the viral model of precellular evolution, the key components of cells 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.