MOLECULAR-CLONING AND CHARACTERIZATION OF THE RIBC GENE FROM BACILLUS-SUBTILIS - A POINT MUTATION IN RIBC RESULTS IN RIBOFLAVIN OVERPRODUCTION

A mutation leading to roseoflavin resistance and deregulated riboflavi n biosynthesis was mapped in the genome of the riboflavin-overproducin g Bacillus subtilis strains RB52 and RB50 at map position 147 degrees. The chromosomal location indicates that the deregulating mutation in RB52 and RB50 is an allele of the previously identified ribC mutation. We cloned the ribC gene and found that it encodes a putative 36-kDa p rotein. Surprisingly, RibC has significant sequence similarity to flav in kinases and FAD synthases from various other bacterial species. By comparing the deduced amino acid sequence of RibC from the wild-type p arent strain of RB50 with the RibC sequence from the riboflavin-overex pressing RB50 mutant we identified a point mutation that resulted in a Gly to Ser exchange in the C-terminal region of the product.