Comparative evolution of the recA gene of surface and deep subsurface microorganisms (an evolutionary clock of intermediate rate). Final report

Because of the ability of the recA protein product to maintain both DNA integrity and increase genetic diversity, this gene may be essential to the survival of microorganisms following the damaging effects of numerous environmental stresses such as exposure to solar UV radiation, exposure to gamma radiation, starvation, and changing environments. While the various activities and amino-acid sequence of recA have been highly conserved among the eubacteria and archaea, little is known as to whether a strict structure-function relationship has been conserved. In other words, are the same regions of this highly plastic, functionally heterogeneous protein involved in the same catalytic capacities throughout the bacterial kingdom? While it is reasonable to assume that this type of conservation has also occurred, we felt it necessary to test the assumption by demonstrating that mutations in different genera of bacteria which eliminate similar functions (i.e., lead to similar phenotypes) are caused by changes in the amino-acid sequence in the same regions of their recA proteins. Therefore, we located the changes in nucleotide sequence in two recA mutants of P. aeruginosa which displayed mutant phenotypes in recombination and UV resistance. Our assumption was that if structure-function relationships held, these mutations would be found in areas already identified as essential for the function of the E. coli recA protein