Organization and transcription of the myo-inositol operon, iol, of Bacillus subtilis

Previous determination of the nucleotide sequence of the ioi region of the Bacillus subtilis genome allowed us to predict the structure of the iol operon for myo-inositol catabolism, consisting of 10 iol genes (iolA to iolJ); iolG corresponds to idh, encoding myo-inositol 2-dehydrogenase (Idh). Primer extension analysis suggested that an inositol-inducible promoter for the iol operon (iol promoter) might be a promoter-like sequence in the 5' region of iolA, which is probably recognized by sigma(A). SB nuclease analysis implied that a rho-independent terminator like structure in the 3' region of iolJ might be a terminator for iol transcription. Disruption of the iol promoter prevented synthesis of the iol transcript as well as that of Idh, implying that the iol operon is most probably transcribed as an 11.5-kb mRNA containing the 10 iol genes. Immediately upstream of the iol operon, two genes (iolR and iolS) with divergent orientations to the iol operon were found. Disruption of iolR (but not iolS) caused constitutive synthesis of the iol transcript and Idh, indicating that the iolR gene encodes a transcription-negative regulator (presumably a repressor) for the iol operon. Northern and S1 nuclease analyses revealed that the iolRS genes were cotranscribed from another inositol-inducible promoter, which is probably recognized by sigma(A). The promoter assignments of the iol and iolRS operons were confirmed in vivo with a lacZ fusion integrated into the amyE locus.