TRANSPOSITION IN LACTOBACILLUS-SAKE AND ITS ABOLITION OF LACTOCIN-S PRODUCTION BY INSERTION OF IS1163, A NEW MEMBER OF THE IS3 FAMILY

This report presents the nucleotide sequence and insertional activity of IS1163, which is a new member of the IS3 family of transposable ele ments. Analysis of spontaneous mutants of the lactocin S-producing Lac tobacillus sake strain L45 show that the bacteriocin-negative phenotyp e is due to either loss of the producer plasmid or the insertion of IS 1163 into the lactocin S operon (las operon). The data further show th at insertional inactivation of the lactocin S operon is the result of a transposition event involving a chromosomally located donor copy of IS1163. Although the insertions described are clustered within a 250-b p region of the las operon, there are no features of the insertion sit es to suggest target-specific insertion of IS1163. The overlapping, fr ameshifted organization of the two major open reading frames found in IS1163 is typical for the IS3 family, but the structure of the putativ e frameshift region includes features which distinguish IS1163 from th e other members of the group. The insertional activity of IS1163 in L. sake L45 has aided in identifying regions of pCIM1 essential for lact ocin S production and may have further practical applications as a mut ational tool in L. sake.