Recombinogenic activity of chimeric recA genes (Pseudomonas aeruginosa/Escherichia coli): A search for RecA protein regions responsible for this activity

In the background of weak, if any, constitutive SOS function, RecA from Pse udomonas aeruginosa (RecAPa) shows a higher frequency of recombination exch ange (FRE) per DNA unit length as compared to RecA from Escherichia coli (R ecAEc). To understand the molecular basis for this observation and to deter mine which regions of the RecAPa polypeptide are responsible for this unusu al activity, we analyzed recAX chimeras between the recAEc and recAPa genes . We chose 31 previously described recombination- and repair-proficient rec AX hybrids and determined their FRE calculated from linkage frequency data and constitutive SOS function expression as measured by using the lacZgene under control of an SOS-regulated promoter. Relative to recAEc, the FRE of recAPa was 6.5 times greater; the relative alterations of FRE for recAX gen es varied from similar to0.6 to 9.0. No quantitative correlation between th e FRE increase and constitutive kSOS function was observed. Single ([L29M] or [II02D]), double ([G136N, V142I]), and multiple substitutions in related pairs of chimeric RecAX proteins significantly altered their relative FRE values. The residue content of three separate regions within the N-terminal and central but not the C-terminal protein domains within the RecA molecul e also influenced the FRE values. Critical amino acids in these regions wer e located close to previously identified sequences that comprise the two su rfaces for Subunit interactions in the RecA polymer. We suggest chat the in tensity of the interactions between the subunits is a key factor in determi ning the FRE promoted by RecA in vivo.