Two regulatory regions controlling basal and cellulose-induced expression of the gene encoding cellobiohydrolase I of...

The cellulolytic system of the filamentous fungus Trichoderma reesei is transcriptionally induced in the presence of the insoluble polymer cellulose. Previous studies have demonstrated that induction of the cellulose transcripts by cellulose requires basal expression of its own genes. To understand how basal expression controls cellulose-induced transcription of those genes, we analyzed the 5'-flanking region of the gene encoding cellobiohydrolase I (cbh1), the major member of the cellulase system, for the cis-acting region that is responsible for regulating basal and cellulose-stimulated expression. Using the promoter deletion approach and an appropriate reporter gene, the cis-acting region responsible for cellulose-stimulated transcription was localized between -241 and -72 bp relative to the TATA box. Deletion of this sequence did not affect the basal expression of the promoter, whereas deletion of 72 bp adjacent to the TATA box abolished basal expression of the cbh1 promoter. We therefore concluded that the cbh1 promoter is composed of two regulatory regions-one controls cellulose-induced transcription and the other is required for its basal expression.