The ribC gene controlling the riboflavin operon in Bacillus subtilis w
as cloned by the resistance to a riboflavin analog 7,8-dimethyl-10-(O-
methylcetoxime)-isoalloxazine. The homology was revealed with the ribo
flavin kinase/FAD synthase gene from Corynebacrerium ammoniagenes and
Escherichia coli. Riboflavin kinase/FAD synthase activity was detected
in cell-free extracts, thus demonstrating that the ribC gene codes fo
r a bifunctional enzyme producing FAD from riboflavin via FMN.