Genetic functions promoting homologous recombination in Escherichia coli: a study of inversions in phage lambda

We have studied homologous recombination in a derivative of phage lambda containing two 1.4-kb repeats in inverted orientation. Inversion of the intervening 2.5-kb segment occurred efficiently by the Escherichia coli RecBC pathway but markedly less efficiently by the lambda Red pathway or the E. coli RecE or RecF pathways. Inversion by the RecBCD pathway was stimulated by Chi sites located to the right of the invertible segment; this stimulation decreased exponentially by a factor of about 2 for each 2.2 kb between the invertible segment and the Chi site. In addition to RecA protein and RecBCD enzyme, inversion by the RecBC pathway required single-stranded DNA binding protein, DNA gyrase, DNA polymerase I and DNA ligase. Inversion appeared to occur either intra- or intermolecularly. These results are discussed in the framework of a current molecular model for the RecBC pathway of homologous recombination.