RecP, a new minor pathway of general recombination in Escherichia coli encoded by plasmid R1drd-19.

Plasmid R1drd-19 markedly improves the recombination deficiency of recB and recBrecC mutants of Escherichia coli K12 as measured by Hfr crosses and increases their resistance to uv inactivation. The effect correlates with the production of an ATP-dependent ds DNA exonuclease in recB/R1drd-19 cells. This paper further investigates the suppressive effect of plasmid R1drd-19 on the recB mutation of E. coli. The gene(s) responsible for the effect was localized to the 13.1-kb EcoRI-C fragment of the resistance transfer factor (RTF) portion of R1drd-19. The plasmid-encoded activity does not merely replace the RecBCD enzyme failure but differs in several significant ways. It promotes a hyper-recombinogenic phenotype, as judged by the phenomenon of super oligomerization of the tester pACYC184 plasmid in recB/R1drd-19 cells and two inter- and intramolecular plasmid recombination test systems. It is probably not inhibited by lambda Gam protein and does not restrict plating of T4gp2 mutant. No significant homology between the E. coli chromosomal fragment carrying recBrecCrecD genes and the EcoRI-C fragment of R1drd-19 was observed. It is suggested that the plasmid-encoded recombination activity is involved in a new minor recombination pathway (designated RecP, for Plasmid). RecP resembles in some traits the RecBCD-independent pathways RecE and RecF but differs in activity and perhaps substrate specificity from the main RecBCD pathway.