EVOLUTIONARY COMPARISONS OF RECA-LIKE PROTEINS ACROSS ALL MAJOR KINGDOMS OF LIVING ORGANISMS

Protein sequences with similarities to Escherichia coli RecA were comp ared across the major kingdoms of eubacteria, archaebacteria, and euka ryotes. The archaeal sequences branch monophyletically and are most cl osely related to the eukaryotic paralogous Rad51 and Dmc1 groups. A mu ltiple alignment of the sequences suggests a modular structure of RecA -like proteins consisting of distinct segments, some of which are cons erved only within subgroups of sequences. The eukaryotic and archaeal sequences share an N-terminal domain which may play a role in interact ions with other factors and nucleic acids. Several positions in the al ignment blocks are highly conserved within the eubacteria as one group and within the eukaryotes and archaebacteria as a second group, but c ompared between the groups these positions display nonconservative ami no acid substitutions. Conservation within the RecA-like core domain i dentifies possible key residues involved in ATP-induced conformational changes. We propose that RecA-like proteins derive evolutionarily fro m an assortment of independent domains and that the functional homolog s of RecA in noneubacteria comprise an array of RecA-like proteins act ing in series or cooperatively.