Molecular Biology

The Evolution of Origins

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Science  06 Apr 2007:
Vol. 316, Issue 5821, pp. 21
DOI: 10.1126/science.316.5821.21b

Prokaryote genomes are generally organized as a single circular chromosome with a single origin of DNA replication; most eukaryotes, on the other hand, have multiple chromosomes, each with multiple replication origins. This latter feature has recently been found in a number of archaea, including Sulfolobus species, which have several origins on a single chromosome. Might these have arisen simply by duplication?

Robinson and Bell show that origins that are conserved across Sulfolobus species share the gene copG, encoding a plasmid copy-number control protein, as well as a number of stress response genes. Furthermore, one of the two origins in the archaeal Aeropyrum pernix bears a striking resemblance to two origins found in a distantly related Sulfolobus species; several genes and evidence of a putative prokaryotic viral integration site are conserved. Among the genes is a protein that is similar to RepA, a bacterial plasmid initiator protein, as well as the yeast replication initiation protein Cdt1. Altogether, this evidence points to a captured extrachromosomal element, possibly a virus/plasmid hybrid, as the source of the supernumerary origins. A hybrid phage/eukaryotic replication initiation site on the yeast 2μ plasmid hints at a similar genesis for the multiple origins on eukaryotic chromosomes. — GR

Proc. Natl. Acad. Sci. U.S.A. 104, 5806 (2007).

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