title: Multiple origins of viral capsid proteins from cellular ancestors.
abstract: Viruses are the most abundant biological entities on earth and show remarkable diversity of genome sequences, replication and expression strategies, and virion structures. Evolutionary genomics of viruses revealed many unexpected connections but the general scenario(s) for the evolution of the virosphere remains a matter of intense debate among proponents of the cellular regression, escaped genes, and primordial virus world hypotheses. A comprehensive sequence and structure analysis of major virion proteins indicates that they evolved on about 20 independent occasions, and in some of these cases likely ancestors are identifiable among the proteins of cellular organisms. Virus genomes typically consist of distinct structural and replication modules that recombine frequently and can have different evolutionary trajectories. The present analysis suggests that, although the replication modules of at least some classes of viruses might descend from primordial selfish genetic elements, bona fide viruses evolved on multiple, independent occasions throughout the course of evolution by the recruitment of diverse host proteins that became major virion components.
authors.affiliation: Institut Pasteur, Department of Microbiology, Unité Biologie Moléculaire du Gène chez les Extrêmophiles, 75015 Paris, France; koonin@ncbi.nlm.nih.gov krupovic@pasteur.fr.
authors.forename: Mart
authors.identifier: 0000-0001-5486-0098
authors.initials: M
authors.lastname: Krupovic
authors.affiliation: National Center for Biotechnology Information, National Library of Medicine, Bethesda, MD 20894 koonin@ncbi.nlm.nih.gov krupovic@pasteur.fr.
authors.forename: Eugene V
authors.initials: EV
authors.lastname: Koonin
mesh_terms: D000818:Animals; D001105:Archaea / Q000235:genetics / Q000378:metabolism / Q000821:virology*; D005075:Biological Evolution; D036022:Capsid Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D056890:Eukaryota / Q000235:genetics / Q000378:metabolism / Q000821:virology*; D016679:Genome, Viral; D006801:Humans; D008958:Models, Molecular; D010802:Phylogeny; D014780:Viruses / Q000737:chemistry / Q000145:classification / Q000235:genetics* / Q000378:metabolism
chemical_list: D036022:Capsid Proteins
keywords: capsid proteins; nucleocapsids; origin of viruses; primordial replicons; virus evolution