LAMBDA-RAP PROTEIN IS A STRUCTURE-SPECIFIC ENDONUCLEASE INVOLVED IN PHAGE RECOMBINATION

Bacteriophage lambda encodes a number of genes involved in the recombi national repair of DNA double-strand breaks. The product of one of the se genes, rap, has been purified. Truncated Rap proteins that copurify with the full-length form are derived, at least in part, from a rho-d ependent transcription terminator located within its coding sequence. Full-length and certain truncated Rap polypeptides bind preferentially to branched DNA substrates, including synthetic Holliday junctions an d D-loops. In the presence of manganese Tons, Rap acts as an endonucle ase that cleaves at the branch point of Holliday and D-loop substrates , It shows no obvious sequence preference or symmetry of cleavage on a Holliday junction, The biochemical analysis of Rap gives an insight i nto how recombinants could be generated by the nicking of a D-loop wit hout the formation of a classical Holliday Junction.