Genetic recombination of bacterial plasmid DNA: electron microscopic analysis of in vitro intramolecular recombination.

a tetramer of pMB9 DNA containing a single EcoRI site per tetramer was used to investigate intramolecular recombination in Escherichia coli. When transformed into wild-type E. coli strains, the tetramer was converted into dimers and a small proportion of trimers and monomers. The conversion was blocked in recA strains and rec B recC recF strains but not in recB recC strains or recF strains. Extracts of E. coli converted the tetramer into dimers, trimers, and monomers. Figure of 8 molecules and catenanes were minor products. The proportion of recombinant molecules ranged from 7% to 14%. Intramolecular recombination in vitro was blocked in extracts of recA strains and recB recC recF strains but not significantly blocked in extracts of recB recC strains and recF strains. recA protein restored activity to recA extracts; activity in recB recC recF extracts was restored by purified exonuclease V (recBC nuclease) or a recF protein donor extract. Novobiocin and oxolinic acid inhibited the reaction by 70-80%.