3.2
Conjugative Transposition of the Sucrose-Nisin Gene Cluster
A genetic linkage between nisin production, nisin immunity and the ability to
use sucrose as a carbon source, was corroborated by the observation that these
properties were transferred in a conjugation-like process [94]. It appeared that
nisin and sucrose genes were clustered on chromosomal elements that were
conjugative transposons [32, 37, 95, 96].
The best characterized conjugative sucrose-nisin transposons are the 70-kb
Tn5276 and Tn5301 [95, 97]. The conjugative transposon Tn5276 and Tn5301
[95, 97] has been found to display a RecA-independent insertion in at least five
different chromosomal sites in derivatives of the L. lactis strain MG1363, but a
single insertion site was preferred and integration of Tn5276 occurred in a
single orientation [97]. The organization of the Tn5276 is given in Fig. 3. The
insertion sequence IS1068 at the left end of Tn5276 was described as an isoIS904
element because of its similarities with IS904, present at the same location in an
other sucrose-nisin conjugative element, Tn5301 [32, 37]. Sucrose-nisin conjugative elements lacking this IS1068 still showed efficient conjugative transposition [37]. It is more likely that the xis/int genes found at the right end of
Tn5276 and shown to be required for the recA-independent excision of Tn5276
ends in E. coli, are involved in site-specific insertion of Tn5276 in Lactococcus
[37, 98]. The int gene could encode a protein of 379 amino acids with homology
to various integrases [98]. The xis gene encodes a small basic protein that
enhances the excision process of Tn5276 [98]. Similar genes are located at the
ends of the conjugative transposons Tn1545/Tn916 [99].
28
E. Sablon et al.
Fig. 2. The primary structure of nisin, a representative of the class IA I lantibiotics
Conjugative Transposition of the Sucrose-Nisin Gene Cluster
A genetic linkage between nisin production, nisin immunity and the ability to
use sucrose as a carbon source, was corroborated by the observation that these
properties were transferred in a conjugation-like process [94]. It appeared that
nisin and sucrose genes were clustered on chromosomal elements that were
conjugative transposons [32, 37, 95, 96].
The best characterized conjugative sucrose-nisin transposons are the 70-kb
Tn5276 and Tn5301 [95, 97]. The conjugative transposon Tn5276 and Tn5301
[95, 97] has been found to display a RecA-independent insertion in at least five
different chromosomal sites in derivatives of the L. lactis strain MG1363, but a
single insertion site was preferred and integration of Tn5276 occurred in a
single orientation [97]. The organization of the Tn5276 is given in Fig. 3. The
insertion sequence IS1068 at the left end of Tn5276 was described as an isoIS904
element because of its similarities with IS904, present at the same location in an
other sucrose-nisin conjugative element, Tn5301 [32, 37]. Sucrose-nisin conjugative elements lacking this IS1068 still showed efficient conjugative transposition [37]. It is more likely that the xis/int genes found at the right end of
Tn5276 and shown to be required for the recA-independent excision of Tn5276
ends in E. coli, are involved in site-specific insertion of Tn5276 in Lactococcus
[37, 98]. The int gene could encode a protein of 379 amino acids with homology
to various integrases [98]. The xis gene encodes a small basic protein that
enhances the excision process of Tn5276 [98]. Similar genes are located at the
ends of the conjugative transposons Tn1545/Tn916 [99].
28
E. Sablon et al.
Fig. 2. The primary structure of nisin, a representative of the class IA I lantibiotics