Linear protein-primed replicating plasmids in eukaryotic microbes.

Klassen R, Meinhardt F

Zusammenfassung

Linear plasmids of eukaryotic microbes are contemporary manifestations of ancient viruses, which have adjusted to two cellular compartments during evolution, i.e., to the mitochondrium or to the cytoplasm. In either case, infectious viral functions do not (any longer) exist. Mitochondrial as well as cytoplasmic elements display aminimized gene equipment and an archetypical mode of replication. Plasmids of filamentous fungi are selfish DNA elements routinely residing in the mitochondria, in which they underwent coevolution with their hosts. In addition to the archetypical viral B-type DNA polymerase, they typically exclusively encode aviral RNA polymerase. Usually, there are neither positive nor negative impacts on their hosts. In afew instances, however, symptoms redolent of amolecular disease, such as the accumulation of defective mitochondria and early onset of senescence, manifest in plasmid-harboring strains. Cytoplasmic localization, which applies for almost all yeast linear plasmids known so far, evidently enforced amore complex enzyme repertoire (of viral origin) to accomplish autonomous extranuclear and extramitochondrial replication and transcription, such as ahelicase, ssDNA binding proteins, and acapping enzyme. Accompanying cytoplasmic plasmids relying functionally on an autonomous element are rather frequent; some encode protein toxins, which benefits the respective host while competing with other yeasts (killer phenotype). Such toxins assure autoselection of the plasmid system as well. Two distinct toxic principles are known up to the present: one was shown to be atRNase, whereas the other clearly involves aDNA-damaging mode of action.

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