Nature of recombinants produced by the RecBC and the RecF pathways in Escherichia coli

Abstract

BASED on analysis of various recombination deficient mutants, at least three different pathways of chromosomal recombination have been suggested in E. coli K12: the RecBC, the RecF and the RecE pathways^1–3. Our present knowledge of initial and final DNA structures and of the intervening events is very limited. Only some of the genes controlling each pathway have been identified^3,4; the products of a few of these have been isolated and characterised^5–10; little is known about the specific steps at which these products participate in the respective pathways. The role of exonuclease V, the product of the recB and recC genes, has been studied^11–15. Recipients deficient in this enzyme give greatly reduced yields of viable recombinants¹¹, but support certain types of recombinational events with relatively high efficiency^12,13,15. ExoV has thus been considered to be more important in determining viability of the recombinant cells than in the recombinational process itself. It has been suggested, on the basis of transformation and transduction experiments, that the recombinant products of the RecBC and the RecF pathways may be structurally different^16,17. We present here results from conjugation crosses of E. coli K12 which demonstrate that the viable recombinants produced by the RecBC and the RecF pathways are significantly different in terms of the density of genetic exchanges present in them. A preliminary account of this work has already been presented¹⁸.