Cloning of ribR, an additional regulatory gene of the Bacillus subtilis riboflavin operon

A 13.0-kb EcoRI fragment of Bacillus subtilis DNA carrying an additional regulatory ribR gene of riboflavin operon was cloned on the basis of resistance to 7, 8-dimethyl-10 (O-methylacetoxym)-isoalloxasin. The cloned fragment was trans-dominant with regard to ribC constitutive mutations that block the overproduction of riboflavin but inactive relative to constitutive mutations in the rib(O) regulatory region.