SummaryThree genes coding for a type I R-M system related to the class C enzymes have been identified on the chromosome of Lactococcus lactis strain IL1403. In addition, plasmids were found that encode only the HsdS subunit that directs R-M specificity. The presence of these plasmids in IL1403 conferred a new R-M phenotype on the host, indicating that the plasmid-encoded HsdS is able to interact with the chromosomally encoded HsdR and HsdM subunits. Such combinational variation of type I R-M systems may facilitate the evolution of their specificity and thus reinforce bacterial resistance against invasive foreign unmethylated DNA.
blL67 is a broad-host-range prolate-headed phage that is active against Lactococcus cells. The complete phage genome sequence of 22 195 bp was established. Thirty-seven open reading frames (ORFs) organized in two clusters were identified. Functions were assigned to the putative products of six of the ORFs on the basis of comparison of the deduced amino acid sequences to known proteins, analysis of structural features of the proteins and search for conserved motifs. These were a DNA polymerase, a protein involved in recombination, a lysin, a terminase subunit, a structural protein and a holin.
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