Organization and expression of a gene cluster involved in the biosynthesis of the lantibiotic lactocin S.

Abstract

Some 8.8 kb of the Lactobacillus sake plasmid pCIM1 was sequenced, revealing eight tightly clustered open reading frames (ORFs) downstream from lasA, which encodes pre-lactocin S. Transcription analyses demonstrated that the genes are expressed as an operon, with transcription initiating upstream of lasA and terminating immediately 3' to the ninth ORF x lasA is also represented by two small RNAs (RNAI and RNAII) which differ in size by approximately 90 nucleotides, and primer extension experiments demonstrated a corresponding difference in the 5' termini. A palindromie sequence constitutes the 3' terminus of both RNAI and RNAII, and we propose that this sequence has a dual regulatory function in controlling the expression of las operon, acting both as a barrier to 3'-5' exonuclease degradation of the lasA-specific transcript(s), and as a "leaky" transcriptional terminator which limits the expression of down-stream genes. Three of the genes in the las operon have identifiable counterparts in other lantibiotic systems: lasM is likely to be involved in prepeptide modification, lasT, which encodes an ATP-dependent transport protein, is probably involved in the secretion of lactocin S, while lasP specifies a subtilisin-type serine protease which may be the lactocin S leader peptidase. Insertional mutation of either lasT or lasM by the resident transposable element IS1163 abolishes lactocin S production. The remaining five ORFs in the las operon are apparently unique, and their significance with respect to the lactocin S phenotype is presently not known.