ScrFI restriction-modification system of Lactococcus lactis subsp. cremoris UC503: cloning and characterization of two ScrFI methylase genes.

Two genes from the total genomic DNA of dairy starter culture Lactococcus lactis subsp. cremoris UC503, encoding ScrFI modification enzymes, have been cloned and expressed in Escherichia coli. No homology between the two methylase genes was detected, and inverse polymerase chain reaction of flanking chromosomal DNA indicated that both were linked on the Lactococcus genome. Neither clone encoded the cognate endonuclease. The DNA sequence of one of the methylase genes (encoded by pCI931M) was determined and consisted of an open reading frame 1,170 bp long, which could encode a protein of 389 amino acids (M(r), 44.5). The amino acid sequence contained the highly characteristic motifs of an m5C methylase. Extensive regions of homology were observed with the methylases of NlaX, EcoRII, and Dcm.