A dual control mechanism synchronizes riboflavin and sulphur metabolism in Bacillus subtilis.

Flavin mononucleotide (FMN) riboswitches are genetic elements, which in many bacteria control genes responsible for biosynthesis and/or transport of riboflavin (rib genes). Cytoplasmic riboflavin is rapidly and almost completely converted to FMN by flavokinases. When cytoplasmic levels of FMN are sufficient ("high levels"), FMN binding to FMN riboswitches leads to a reduction of rib gene expression.