Riboflavin operon of Bacillus subtilis: unusual symmetric arrangement of the regulatory region.

Seventeen cis-dominant mutations leading to riboflavin overproduction in Bacillus subtilis were localized to the region between nucleotides +37 and +159 relative to the transcription initiation site of the riboflavin operon. This region displays an unusual structure for regulatory sequences. The main part of it represents clusters of A/T and G/C-rich sequences that symmetrically blank a short inverted repeat.