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Appl. Environ. Microbiol., Dec 1995, 4321-4328, Vol 61, No. 12
P Garvey, GF Fitzgerald and C Hill
The lactococcal plasmid pNP40, from Lactococcus lactis subsp. lactis biovar
diacetylactis DRC3, confers complete resistance to the prolate- headed
phage phi c2 and the small isometric-headed phage phi 712 in L. lactis
subsp. lactis MG1614. A 6.0-kb NcoI fragment of pNP40 cloned in the
lactococcal Escherichia coli shuttle vector pAM401 was found to confer
partial resistance to phi 712. Subcloning and deletion analysis of the
recombinant plasmid pPG01 defined a 2.5-kb ScaIHpaI fragment as conferring
phage insensitivity. Sequence analysis of this region confirmed the
presence of two overlapping open reading frames (ORFs). Further subcloning
of pNP40 to characterize the resistance determinant active against phi c2
identified a 5.6-kb EcoRV fragment of pNP40 which, when cloned in pAM401,
conferred partial resistance to both phi c2 and phi 712. Subcloning and
deletion analysis of the recombinant plasmid pCG1 defined a 3.7-kb
EcoRV-XbaI fragment as encoding phage insensitivity. DNA sequence analysis
of this region revealed the presence of a single complete ORF. The
introduction of a frameshift mutation at the unique BglII site within this
ORF disrupted the phage resistance phenotype, confirming that this ORF is
responsible for the observed phage insensitivity. The mechanisms encoded by
pPG01 and pCG1 in L. lactis subsp. lactis MG1614 conformed to the criteria
defining abortive infection and were designated AbiE and AbiF,
respectively. Analysis of the phage DNA content of phi 712-infected hosts
containing AbiF demonstrated that it inhibited the rate of phage DNA
replication, while AbiE had little effect on phage DNA replication,
suggesting a later target of inhibition. The predicted protein product of
abiF shows significant homology to the products of two other lactococcal
abortive infection genes, abiD and abiD1.
Copyright © 1995, American Society for Microbiology
Cloning and DNA sequence analysis of two abortive infection phage resistance determinants from the lactococcal plasmid pNP40
Department of Microbiology, University College, Cork, Ireland.
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