Abstract
Difficulties in replication can lead to breakage of the fork. Recombinational reactions restore the integrity of the fork through strand-invasion of the broken chromosome with its sister. If this occurs in the context of repeated DNA sequences, genetic rearrangements can result. We have proposed that this process accounts for stimulation of chromosomal rearrangements by mutations in
Escherichia coli's replicative DNA helicase, DnaB. At its permissive temperature for growth, a
dnaB107 mutant is a 1000-fold more likely to experience a deletion of a 787
bp tandem repeated segment inserted in the
E. coli chromosome than is a wild-type strain. We have previously shown that enhanced deletion in a
dnaB107 strain is reduced in
recA,
recB and
recG102 (formerly known as
radC102) derivatives. Here I show that this enhanced recombination is dependent on other factors: the RuvA Holliday junction helicase, the RecJ single-strand DNA exonuclease, the RadA/Sms RecA-paralog protein of unknown function and, surprisingly, the DinB translesion polymerase. The requirement for these factors in DnaB-stimulated rearrangements is much greater than that observed for recombinational events such as P1 transduction. This may be because strand invasion into the repeats limits the extent of heteroduplex DNA that can be formed in the initial stage of recombination. I propose that RadA, RecG and RuvAB are critically required to stabilize the strand-invasion intermediate and that DinB polymerase extends the invading 3′ strand to aid in re-initiation. The role of DinB in bacteria may be analogous to translesion DNA polymerase η in eukaryotes, recently shown to aid recombination.