Summary: The DNA regions upstream from the genes encoding polypeptides of subsp. larvicidal crystals contain sequences with similarities to the box of (or ‘OA’ box) and the promoter recognized by the σ-associated RNA polymerase of . Expression of transcriptional fusions was analysed in various genetic backgrounds. The early transcription of the toxin genes was not sporulation-dependent, whereas the late-stage expression at was σ-dependent. Primer extension analysis confirmed that the -and -type toxin genes were weakly transcribed during the transition phase; expression analysis of a '-lacZ transcriptional fusion in sporulation mutants confirmed the involvement of the σ-RNA polymerase. Primer extension analysis showed that in subsp. , the and gene transcription observed at the end of the growth stage was turned off at the beginning of the sporulation phase. The DNA region located upstream from the gene promoter including the putative ‘OA’ box was deleted. This led to a derepression of the expression of the operon. These results suggest that the and toxin genes of subsp. are transcribed during the transition phase by the RNA polymerase associated with the σ factor and are subject to SpoOA repression.


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