ORGANIZATION AND TRANSCRIPTION OF THE MYOINOSITOL 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 t he iol operon for myo-inositol catabolism, consisting of 10 iol genes (iolA to iolJ); iolG corresponds to idh, encoding myo-inositol 2-dehyd rogenase (Idh). Primer extension analysis suggested that an inositol-i nducible promoter for the iol operon (iol promoter) might be a promote r-like sequence in the 5' region of iolA, which is probably recognized by sigma(A). SB nuclease analysis implied that a rho-independent term inator like structure in the 3' region of iolJ might be a terminator f or iol transcription. Disruption of the iol promoter prevented synthes is 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. D isruption of iolR (but not iolS) caused constitutive synthesis of the iol transcript and Idh, indicating that the iolR gene encodes a transc ription-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 prob ably recognized by sigma(A). The promoter assignments of the iol and i olRS operons were confirmed in vivo with a lacZ fusion integrated into the amyE locus.