The synthesis of the Streptomyces reticuli cellulase (Avicelase) is regulated by both activation and repression mechanisms

Abstract

The Streptomyces reticuli cellulase (Cell, Avicelase) hydrolyzes crystalline cellulose (Avicel) efficiently to cellobiose. The synthesis of the enzyme is induced by Avicel and repressed by glucose. DNA-binding proteins were purified from induced S. reticuli mycelia by affinity chromatography using the upstream region of the cel1 gene linked to Sepharose. The enriched protein(s) provoked a gel electrophoresis mobility shift of the upstream region, irrespective of the presence or absence of a 14-bp palindromic sequence, and enhanced the transcription of the cel1 gene by the S. reticuli RNA polymerase in vitro. The binding site (GTGACTGAGCGCCG) for the protein(s) was located in the vicinity of a DNA bend upstream of the transcriptional start site. Results of physiological studies, deletion and gel-shift analyses lead to the conclusion that a 14-bp palindrome (TGGGAGCG CTCCCA) - situated between the transcriptional start site and the structure gene - is the operator for a repressor protein. The data presented suggest that the two identified cis-acting elements, in cooperation with an activator and a repressor, mediate regulation of cel1 transcription.