Nisin produced by Lactococcus lactis 6F3 is used as a food preservative and is 
the most important member of a group of peptide-antibiotics containing 
lanthionine bridges (lantibiotics) (N. Schnell, K.-D. Entian, U. Schneider, F. 
Götz, H. Zähner, R. Kellner, and G. Jung, Nature [London] 333:276-278, 1988). 
Nisin is ribosomally synthesized, and its structural gene, nisA, encodes a 
prepeptide that is posttranslationally modified, revealing the active 
lantibiotic (C. Kaletta and K.-D. Entian, J. Bacteriol. 171:1597-1601, 1989). 
Adjacent to nisA, the additional genes nisB, nisT, and nisC were identified. 
Over their entire sequences, these genes were homologous to genes recently 
identified as important for the biosynthesis of lantibiotics, that is, subtilin 
from Bacillus subtilis ATCC 6633 and epidermin from Staphylococcus epidermidis 
Tü 3298. Genes nisB, nisT, and nisC corresponded to open reading frames of 993, 
600, and 418 amino acid residues, respectively. The nisT open reading frame is 
homologous to proteins of the HlyB (hemolysin B protein of Escherichia coli) 
subfamily. Proteins of this subfamily are responsible for the secretion of a 
variety of compounds, including large polypeptides, polysaccharides, and 
anti-drug tumors, indicating that NisT may be involved in nisin transport. 
Northern (RNA) blot analysis revealed a 0.3-kb transcript for the nisA 
structural gene, and the transcriptional start point of the nisA gene was 
determined by primer extension. Additionally, a mRNA of at least 3 kb was 
identified by using a hybridization probe specific to nisB. Antibodies were 
raised against the NisB protein, and Western blot (immunoblot) analysis revealed 
a molecular weight of about 115 kDa, which is in accordance with the theoretical 
protein size of 117.5 kDa as calculated from the nisB open reading frame. 
Several amphipathic transmembrane alpha-helices indicated that NisB is 
associated with the membrane. This was confirmed by preparing L. lactis 
vesicles. The NisB protein was tightly associated with the vesicle fraction and 
was released by sodium dodecyl sulfate treatment only. These results suggest 
that NisB is membrane associated and that nisin biosynthesis occurs at the cell 
membrane.