GENETIC-MAPPING OF AN ADDITIONAL REGULATO RY LOCUS OF THE BACILLUS-SUBTILIS RIBOFLAVIN OPERON

Two mutations designated ribR5 and ribR6, which effectively decrease t he constitutive expression of the Ba cillus subtilis riboflavin operon , were mapped in the 236 degrees region of the B. subtilis genetic map based on linkage analysis with respect to the apt6 marker. Cotransfer indices for the ribR5 and ribR6 markers and apt6 suggest that both ri hR mutations are alleles of exactly the same genetic locus. Total resu lts of transductional and transformational crosses indicate the follow ing marker order: pheA-apt6-ribR-azlB-aroD4. Phenotypic peculiarities of the ribR mutants allow us to assume that they belong to an addition al subunit of the regulatory protein of the riboflavin operon.