Distinguishing Characteristics of Hyperrecombinogenic RecA Protein from Pseudomonas aeruginosa Acting in Escherichia coli

Abstract

ABSTRACT In Escherichia coli , a relatively low frequency of recombination exchanges (FRE) is predetermined by the activity of RecA protein, as modulated by a complex regulatory program involving both autoregulation and other factors. The RecA protein of Pseudomonas aeruginosa (RecA Pa ) exhibits a more robust recombinase activity than its E. coli counterpart (RecA Ec ). Low-level expression of RecA Pa in E. coli cells results in hyperrecombination (an increase of FRE) even in the presence of RecA Ec . This genetic effect is supported by the biochemical finding that the RecA Pa protein is more efficient in filament formation than RecA K72R, a mutant protein with RecA Ec -like DNA-binding ability. Expression of RecA Pa also partially suppresses the effects of recF , recO , and recR mutations. In concordance with the latter, RecA Pa filaments initiate recombination equally from both the 5′ and 3′ ends. Besides, these filaments exhibit more resistance to disassembly from the 5′ ends that makes the ends potentially appropriate for initiation of strand exchange. These comparative genetic and biochemical characteristics reveal that multiple levels are used by bacteria for a programmed regulation of their recombination activities.