Transposition in Lactobacillus sakei: inactivation of a second lactocin S operon by the insertion of IS1520, a new member of the IS3 family of insertion sequences.

The analysis of spontaneous bacteriocin-negative mutants has led to the identification and characterization of a new, transpositionally active, insertion sequence of the IS3 family in the lactocin-S-producing Lactobacillus sakei strain L45. The element, which has been designated IS1520, is 1302 bp long with 10 bp perfect inverted repeat ends and generates direct repeats of a trinucleotide of target sequence upon transposition to the lactocin S locus. IS1520 encodes two consecutive, partially overlapping, major ORFs, which are frameshifted in a manner typical of the IS3 family. Despite a low overall DNA sequence similarity, the putative frameshifting region of IS1520 is highly similar to the corresponding region of IS1163, which is a related element previously shown to be active in L. sakei L45.