1997 Volume 43 Issue 2 Pages 67-73
A 56-kb plasmid was identified in Lactococcus lactic subsp. lactis (L. lactis) M189 which encodes resistance to nisin (NisR) following mobilization of the plasmid into L. lactis LM0230. The NisR determinant was localized on a 1.6-kb Hindlll fragment by DNA restriction fragment deletion and subcloning. An open reading frame (ORF) of 957 bases was identified by sequence analysis and its transcription start site was mapped by primer extension. The ORF is flanked by two regions which exhibit complete homology to parts of the inverted repeat sequences of IS981 and ISS1T. The promoter for transcription was found to consist of an extended -10 site (TgTGtTATAAT) that lacks a -35 site. Function of the extended -10 promoter was demonstrated by its ability to express the promoterless cat gene from Staphylococcus aureus. Base substitution analysis revealed that the TgTGt extension is essential for promoter efficiency in L. lactis.