Dual effect of a Tn917 insertion into the Bacillus subtilis sacX gene.

The most common effect of transposon insertion is the inactivation of genes. However, in some cases, transposons can activate in cis the expression of genes in the neighbourhood of their integration site. We previously described an insertion of the transposon Tn917 into the Bacillus subtilis sacXY locus. sacX and sacY encode respectively a negative and a positive regulator involved in induction by sucrose of the exoenzyme levansucrase. Data in this paper show that the Tn917 insertion had two effects: it inactivated sacX and it increased the transcription of sacY. The latter effect involved one or several elements internal to the transposon.