IDENTIFICATION OF A RECA HOMOLOG (RECA(LP)) ON THE CONJUGATIVE LACTOCOCCAL PHAGE RESISTANCE PLASMID PNP40 - EVIDENCE OF A ROLE FOR CHROMOSOMALLY ENCODED RECA(L) IN ABORTIVE INFECTION

The determinants for two bacteriophage resistance mechanisms, AbiE and AbiF, are separated by approximately 3,300 nucleotides on the lactoco ccal plasmid pNP40 (P. Garvey, G. F. Fitzgerald, and C. Hill, Appl. En viron, Microbiol, 61:4321-4328, 1995), DNA sequence analysis of the in tervening region led to the identification of two open reading frames (ORFs) which are transcribed in the opposite direction to the Abi dete rminants, One of these ORFs encodes a recA homolog (designated recA(LP )), This is the first report of a recA-like determinant located to a p lasmid, The second ORF (orfU) shares homology with the umuC gene of th e SOS response, Analysis of a number of lactococcal strains confirmed the presence of recA(LP)-like sequences in at least two other lactococ cal strains, The proximity of the recA and umuC homologs suggested a p ossible role in the phage resistance encoded by the Abi determinants, However, no evidence was obtained to demonstrate a function for either ORF in the expression of either AbiE or AbiF, Nor could the recA(LP) gene restore resistance to mitomycin in a recA-deficient lactococcal s train, VEL1122, Interestingly, it was shown that the chromosomally enc oded recA is necessary for complete expression of the AbiF phenotype, confirming a role for RecA in this abortive infection system.