Characterization of a novel plasmid-encoded HsdS subunit, S.LlaW12I, from Lactococcus lactis W12.

A novel type I restriction-modification specificity subunit, S. LlaW12I, has been identified on the naturally occurring 8.0-kb plasmid pAW122 in the lactic acid bacterium Lactococcus lactis subsp. cremoris W12. Presence of the HsdS protein together with a complete type I restriction-modification system conferred increased phage restriction to the host, indicating exchange of specificity subunits. Sequence analysis showed that the S.LlaW12I subunit is most probably of type IC. Presumably, the hsdS gene is organized together with the repB gene on one transcriptional unit.
(Copyright 2000 Academic Press.)