An mRNA structure that controls gene expression by binding FMN

Abstract
The RFN element is a highly conserved domain that is found frequently in the 5′-untranslated regions of prokaryotic mRNAs that encode for flavin mononucleotide (FMN) biosynthesis and transport proteins. We report that this domain serves as the receptor for a metabolite-dependent riboswitch that directly binds FMN in the absence of proteins. Our results also indicate that in Bacillus subtilis , the riboswitch most likely controls gene expression by causing premature transcription termination of the ribDEAHT operon and precluding access to the ribosome-binding site of ypaA mRNA. Sequence and structural analyses indicate that the RFN element is a natural FMN-binding aptamer, the allosteric character of which is harnessed to control gene expression.