Article Abstract:
The genetic coding for the type II restriction-modification (R/M) system LlaBI, s bacteriophage resistance system, are cloned from the plasmid of Lactococcus lactis subsp. cremoris W56 and sequenced for their nucleotides. Sequence analysis indicates the presence of an endonuclease consisting of 299 amino acids and a methylase with 580 amino acids. The presence of a 4.0-kb HindIII fragment in pSA3, which can restrict bacteriophages, shows that the cloned R/M system serves as a phage defense mechanism in L. lactis.
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Article Abstract:
Experiments were conducted to identify a type II restriction/modification (R/M) system in the naturally occurring 8.9-kb plasmid pHW393 in Lactococcus lactis subspecies cremoris. The Lactococcus species was obtained from a mixed cheddar starter resistant to bacteriophages and was cotransformed with the marker plasmid pVS2 into phage-sensitive and plasmid-free strain of L. lactis. The ability of the Lla R/M system to function as a defense mechanism against seven phages was also examined.
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Article Abstract:
Studies done to identify genes responsible for host recognition in the lactococcal phages sk1 and bIL170 belonging to species 936 are reported. The results of the studies strongly suggest that homologous genes, orf18 in phage sk1 and orf20 in phage bIL170 encode receptor-binding protein (RBPs). Moreover, two groups of lytic lactococcal phages pertaining to species 936 were identified based on host specificity, host binding ability, and the amino acid sequence of the RBP.
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