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

Abstract
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/Grich sequences that symmetrically blank a short inverted repeat.