two gene products are required for activity, and lactococcin M was classified as
a class IIB bacteriocin according to the classification of Nes et al. [128] (1995).
Cloning and sequence analysis of the region downstream from lactococcin A
identified a third lactococcin operon, designated as LcnB and its immunity
protein LciB [136]. Site-directed mutagenesis showed that LciA and LciM were
essential for producer strain immunity but did not cross-protect against the
other bacteriocins [46]. Lactococcin A, produced by L. lactis subsp. cremoris
LMG2130 was independently purified and sequenced [125]. The structural gene
was mapped to a 55-kb conjugal plasmid of the producer strain and DNA
sequencing revealed that this lactococcin was identical to the high activity
lactococcin A, cloned and sequenced by van Belkum et al. [135].
32
E. Sablon et al.
Fig. 4. Representative class II non-lantibiotic bacteriocin operons. The class II non-lantibiotic bacteriocins include lactococcin A, B, M and G [46, 125, 126, 128, 135, 136], lactacin F [77],
pediocin PA-1 and AcH [62, 130, 131], mesentericin Y105 [124], sakacin A [133] and plantaricin A [49, 134]. The structural genes are high1ighted as black arrowheads. Genes with
similar proposed function or substantial sequence similarity are highlighted in the same
manner. The arrowheads indicate the direction of transcription. The function of MesC, and
SapOSTUV of the mesentericin Y150 and plantaricin A operons is unknown