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Appl. Environ. Microbiol., 04 1997, 1244-1251, Vol 63, No. 4
P Garvey, A Rince, C Hill and GF Fitzgerald
The determinants for two bacteriophage resistance mechanisms, AbiE and
AbiF, are separated by approximately 3,300 nucleotides on the lactococcal
plasmid pNP40 (P. Garvey, G.F. Fitzgerald, and C. Hill, Appl. Environ.
Microbiol. 61:4321-4328, 1995). DNA sequence analysis of the intervening
region led to the identification of two open reading frames (ORFs) which
are transcribed in the opposite direction to the Abi determinants. One of
these ORFs encodes a recA homolog (designated recALP). This is the first
report of a recA-like determinant located to a plasmid. The second ORF
(orfU) shares homology with the umuC gene of the SOS response. Analysis of
a number of lactococcal strains confirmed the presence of recALP-like
sequences in at least two other lactococcal strains. The proximity of the
recA and umuC homologs suggested a possible role in the phase 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 recALP gene restore resistance to mitomycin in a
recA-deficient lactococcal strain, VEL1122. Interestingly, it was shown
that the chromosomally encoded recA is necessary for complete expression of
the AbiF phenotype, confirming a role for RecA in this abortive infection
system.
Copyright © 1997, American Society for Microbiology
Identification of a recA homolog (recALP) on the conjugative lactococcal phage resistance plasmid pNP40: evidence of a role for chromosomally encoded recAL in abortive infection
Department of Microbiology, University College, Cork, Ireland.
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