dominantly hydrophobic proteins with three or four potential transmembrane
domains, described to play a role in immunity to colicins [111, 112]. Approximately 1 kb downstream from nisG, three more open reading frames with
an opposite orientation were observed. The largest protein of 318 amino acids
shows similarities with the helix-loop-helix type of DNA binding proteins, and
its N-terminus of 27 amino acids was identical to the SacR regulatory protein
[104]. The two further open reading frames showed homology to the lactococcal insertion element, IS981 [104].
Based on DNA homology, five different promoter regions were identified in
the nisin gene cluster in front of nisB, nisT, nisC, nisR and nisF and two potential transcription terminators downstream from nisB and nisK [100, 104, 113,
114]. The promoter preceding nisA and the promoter upstream from nisR [103]
both display characteristics of positively regulated promoters [114]. The intergenic region between nisA and nisB contains an inverted repeat that could
act as a transcription terminator [91], transcription attenuator [103], or a signal
for internal processing between the nisA/Z and nisB gene [115]. Recent studies showed that the nisZBTCIPRKFEG gene cluster consists of at least two operons resulting in a nisZBTCIPRK and a nisFEG transcript [115, 116]. The
nisZBTCIPRK transcript is processed downstream from the structural nisZ
gene [115]. Both promoters were inducible by raising of extracellular nisin
concentrations, suggesting that nisin biosynthesis and immunity were autoregulated [115].
The sac genes, encoded by the Tn5276 conjugative transposon in the opposite
orientation of the nisin gene cluster are involved in sucrose metabolism and
organized in two divergent operons with a back-to-back configuration [97].
Both operons are controlled by a sucrose-inducible promoter [97] and result in
a rightward transcript, containing the sacBK (sucrose-specific PTS enzyme II
and a putative fructose kinase) genes and a leftward transcript, containing the
sacAR (sucrose-6-phosphate hydrolase and a putative regulator) genes [103].
3.4
The Class IA II Lantibiotics Lactococcin DR and Lactocin S
Besides nisin, three other lantibiotics produced by LAB, namely lactococcin DR
(= lacticin 481) [30, 117–119], lactocin S [31, 33, 82] and carnocin U-I49 [35,
36, 120] have been reported, but only the first two were genetically studied in
more detail (Fig. 3) [82, 118–121]. Both lactocin S and lactococcin DR are
members of the class IA II lantibiotics. Lantibiotics of this class have a divergent
leader peptide compared with the class IA I lantibiotics represented by nisin, but
also their genetical organization differs significantly from that of the class IA I
lantibiotics [40, 82].
Downstream from the structural lacticin 481 (= lactococcin DR) gene, lctA
(= lcnDR1), lctM (= lcnDR2) encoded a protein of 922 amino acids [82, 118]. A
925-residue protein (LasM) with striking homology to LctM, was encoded
downstream from the structural lactocin S gene [82], and cylM, a 993-amino
acid residue protein was shown for the non-lactic acid bacteria lantibiotic,
cytolysin [122]. This protein family is typical for the class IA II lantibiotics, and
30
E. Sablon et al.
domains, described to play a role in immunity to colicins [111, 112]. Approximately 1 kb downstream from nisG, three more open reading frames with
an opposite orientation were observed. The largest protein of 318 amino acids
shows similarities with the helix-loop-helix type of DNA binding proteins, and
its N-terminus of 27 amino acids was identical to the SacR regulatory protein
[104]. The two further open reading frames showed homology to the lactococcal insertion element, IS981 [104].
Based on DNA homology, five different promoter regions were identified in
the nisin gene cluster in front of nisB, nisT, nisC, nisR and nisF and two potential transcription terminators downstream from nisB and nisK [100, 104, 113,
114]. The promoter preceding nisA and the promoter upstream from nisR [103]
both display characteristics of positively regulated promoters [114]. The intergenic region between nisA and nisB contains an inverted repeat that could
act as a transcription terminator [91], transcription attenuator [103], or a signal
for internal processing between the nisA/Z and nisB gene [115]. Recent studies showed that the nisZBTCIPRKFEG gene cluster consists of at least two operons resulting in a nisZBTCIPRK and a nisFEG transcript [115, 116]. The
nisZBTCIPRK transcript is processed downstream from the structural nisZ
gene [115]. Both promoters were inducible by raising of extracellular nisin
concentrations, suggesting that nisin biosynthesis and immunity were autoregulated [115].
The sac genes, encoded by the Tn5276 conjugative transposon in the opposite
orientation of the nisin gene cluster are involved in sucrose metabolism and
organized in two divergent operons with a back-to-back configuration [97].
Both operons are controlled by a sucrose-inducible promoter [97] and result in
a rightward transcript, containing the sacBK (sucrose-specific PTS enzyme II
and a putative fructose kinase) genes and a leftward transcript, containing the
sacAR (sucrose-6-phosphate hydrolase and a putative regulator) genes [103].
3.4
The Class IA II Lantibiotics Lactococcin DR and Lactocin S
Besides nisin, three other lantibiotics produced by LAB, namely lactococcin DR
(= lacticin 481) [30, 117–119], lactocin S [31, 33, 82] and carnocin U-I49 [35,
36, 120] have been reported, but only the first two were genetically studied in
more detail (Fig. 3) [82, 118–121]. Both lactocin S and lactococcin DR are
members of the class IA II lantibiotics. Lantibiotics of this class have a divergent
leader peptide compared with the class IA I lantibiotics represented by nisin, but
also their genetical organization differs significantly from that of the class IA I
lantibiotics [40, 82].
Downstream from the structural lacticin 481 (= lactococcin DR) gene, lctA
(= lcnDR1), lctM (= lcnDR2) encoded a protein of 922 amino acids [82, 118]. A
925-residue protein (LasM) with striking homology to LctM, was encoded
downstream from the structural lactocin S gene [82], and cylM, a 993-amino
acid residue protein was shown for the non-lactic acid bacteria lantibiotic,
cytolysin [122]. This protein family is typical for the class IA II lantibiotics, and
30
E. Sablon et al.