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Structural homologies among different restriction systems of Escherichia coli and several Salmonella species have been investigated by immunological methods using antibodies prepared against two subunits of the E. coli K12 restriction enzyme, and by DNA hybridization experiments using different fragments of the E. coli K12 hsd genes as probes. The results with both techniques show a strong homology between the E. coli K12 and B restriction‐modification systems, weaker but nevertheless marked homology between E. coli K12 and the Salmonella systems SB, SP, and SQ and, surprisingly, no homology between the E. coli K12 and A systems.

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been isolated. It proves to be an unusual enzyme, clearly related functionally to the classical type I restriction enzymes. The basic enzyme is a two subunit modification methylase. Another protein species can be purified which by itself has no enzymatic activities but which converts the modification methylase to an ATP and S-adenosylmethionine-dependent restriction endonuclease. The DNA recognition sequence of EcoA has an overall structure that is very similar to previously determined type I sequences. It is: 5'-GAGNNNNNNNGTCA-3' 3'-CTCNNNNNNNCAGT-5' where N can be any nucleotide. Modification methylates the adenosyl residue in the specific trinucleotide and the adenosyl residue in the lower strand of the specific tetranucleotide.

A new lanthionine-containing bacteriocin, variacin, displaying a broad host range of inhibition against gram-positive food spoilage bacteria, has been identified from two strains of Micrococcus varians isolated from meat fermentations. The new bacteriocin was purified, and its amino-terminal end and total amino acid composition were determined. The structural gene was isolated and analyzed. Variacin is resistant to heat and pH conditions from 2 to 10. Its primary sequence shows significant homology to lacticin 481 of Lactococcus lactis, which is more pronounced for the probacteriocin than for the leader sequence. Variacin, like lacticin 481, contains lanthionine and ␤-methyllanthionine residues, but its leader sequence clearly resembles nonlantibiotic leader sequences. In particular, the prepeptide contains glycine residues at positions ؊1 and ؊2 of the processing site.