THE RECA PROTEIN AS A MODEL MOLECULE FOR MOLECULAR SYSTEMATIC STUDIESOF BACTERIA - COMPARISON OF TREES OF RECAS AND 16S RIBOSOMAL-RNAS FROM THE SAME SPECIES

The evolution of the RecA protein was analyzed using molecular phyloge netic techniques. Phylogenetic trees of all currently available comple te RecA were inferred using multiple maximum parsimony and distance ma trix methods. Comparison and analysis of the trees reveal that the inf erred relationships among these proteins are highly robust. The RecA t rees show consistent subdivisions corresponding to many of the major b acterial groups found in trees of other molecules including the alpha, beta, gamma, delta, epsilon proteobacteria, cyanobacteria, high-CC gr am-positives, and the Deinococcus-Thermus group. However, there are in teresting differences between the RecA trees and these other trees. Fo r example, in all the RecA trees the proteins from gram-positive speci es are not monophyletic. In addition, the RecAs of the cyanobacteria c onsistently group with those of the high-GC gram-positives. To evaluat e possible causes and implications of these and other differences phyl ogenetic trees were generated for small-subunit rRNA sequences from th e same (or closely related) species as represented in the RecA analysi s. The trees of the two molecules using these equivalent species-sets are highly congruent and have similar resolving power for close, mediu m, and deep branches in the history of bacteria. The implications of t he particular similarities and differences between the trees are discu ssed. Some of the features that make RecA useful for molecular systema tics and for studies of protein evolution are also discussed.