Genetic Exchange in Bacteriophages
Genetic recombination supplies the machinery to rearrange DNA segments, creating new phages with new gene combinations by loss or gain of function. Phages such as lambda carry their own genes for initiating and completing exchange. Lambda exonuclease (Exo) processes double-stranded DNA ends, while Bet participates in annealing the resulting single-stranded product to homologous sequences. Lambda encodes a third polypeptide, NinB (Orf), that assists in the early stages of recombinational exchange by binding single-stranded DNA. NinB is required for lambda recombination in the absence of either of three much larger E. coli recombination proteins, RecF, RecO and RecR. RecFOR are implicated in loading other recombination proteins onto DNA Experiments are underway to investigate any interactions between NinB and other host and phage recombination proteins. Exchange is completed by elimination of the branched DNA structures by the Rap endonuclease, another enzyme being studied in our laboratory.