Evolution

Breaking Down the Tree of Life

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Science  30 Jun 2006:
Vol. 312, Issue 5782, pp. 1849
DOI: 10.1126/science.312.5782.1849b

Double-stranded breaks in DNA are repaired by members of the recA/RAD51 gene family. The resolution of these breaks through crossover events is also important in creating genetic diversity. Eubacteria have a single recA homolog, whereas eukaryotes and archaea have at least two each.

Lin et al. have surveyed the evolutionary history of the recA/RAD51 gene family and traced three major lineages: the RADα and RADβ subfamilies that are found only in archaea and eukaryotes, and the recA subfamily that is found in eubacteria as well as in plants and protists (possibly introduced via horizontal gene transfer from the organelles). This suggests that the original recA/RAD51 gene existed in the ancestor of all cellular organisms, with a single copy maintained within the eubacteria. In contrast, gene duplications in the common ancestor of eukaryotes and archaea resulted in the RADα and RADβ subfamilies, which experienced further gene duplications before the diversification of animals and plants. The authors propose that the origin and retention of multiple recA homologs may represent evolutionary innovations that contributed to the success of the eukaryotes. — LMZ

Proc. Natl. Acad. Sci. U.S.A. 103, 10.1073/pnas.0604232103 (2006).

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