Structure and regulation of controlling sequences for the Streptomyces coelicolor glycerol operon.

The pathway for glycerol catabolism in Streptomyces coelicolor is determined by the gylABX operon. The sequence of about 1500 base-pairs (bp) preceding the structural genes of the operon has been determined, and related to a detailed transcriptional analysis of this region. The gylABX operon contains two major promoters, gylP1 and gylP2, separated by 50 bp. Both promoters are glycerol-inducible and glucose-repressible. A 900-base transcription unit, gylR, is situated immediately upstream of the gylABX promoter region and contains an open reading frame for a 27,600 Mr protein. The predicted sequence of this protein contains a region that is similar to the helix-turn-helix domains of certain DNA-binding proteins. Transcription of gylR is also glycerol-inducible, but is only weakly glucose-repressible, and initiates predominantly from a single promoter, gylRp. The three promoters, gylRP, gylP1 and gylP2, each resemble the "typical" prokaryotic consensus promoter sequence. The DNA sequence of the gylR and gylABX promoter regions share some striking features. These include almost identical operator-like elements (segments of which are tandemly repeated around gylRP) and tracts of alternating purine-pyrimidine residues.