FUNCTIONAL-ORGANIZATION OF THE RIBOFLAVIN BIOSYNTHESIS OPERON FROM BACILLUS-SUBTILIS SHGW

We have sequenced 6006 bp DNA of a region from the Bacillus subtilis S Hgw chromosome known to contain riboflavin biosynthesis genes (rib gen e cluster, 210 degrees on the B. subtilis genetic map). Five of the se ven open reading frames found within the sequence are shown to represe nt the genes ribG, ribB, ribA, ribH and ribTD. The calculated molecula r masses for the putative translation products are 39305, 23481, 44121 , 16287 and 14574 daltons respectively. The five rib genes are transcr ibed as a polycistronic 4277 nucleotide messenger RNA. The steady-stat e level of the transcript is negatively regulated by riboflavin. A cis -acting element necessary for regulation was mapped by analysis of con stitutive mutations within the 5' untranslated region of the operon. T he element is at least 48 bp in length and does not bear obvious simil arity to well defined prokaryotic regulatory elements. The molecular m echanism of regulation remains unknown, but the data presented argue a gainst regulation by attenuation.