The role of CRE1 in nucleosome positioning within the cbh1 promoter and coding regions of Trichoderma reesei

Nucleosome positioning within the promoter and coding regions of the cellobiohydrolase-encoding cbh1 gene of Trichoderma reesei was investigated. T. reesei is a filamentous fungus that is able to degrade dead plant biomass by secreting enzymes such as cellulases, a feature which is exploited in industrial applications. In the presence of different carbon sources, regulation of one of these cellulase-encoding genes, cbh1, is mediated by various transcription factors including CRE1. Deletion or mutation of cre1 caused an increase in cbh1 transcript levels under repressing conditions. CRE1 was shown to bind to several consensus recognition sequences in the cbh1 promoter region in vitro. Under repressing conditions (glucose), the cbh1 promoter and coding regions are occupied by several positioned nucleosomes. Transcription of cbh1 in the presence of the inducer sophorose resulted in a loss of nucleosomes from the coding region and in the re-positioning of the promoter nucleosomes which prevents CRE1 from binding to its recognition sites within the promoter region. Strains expressing a non-functional CRE1 (in strains with mutated CRE1 or cre1-deletion) exhibited a loss of positioned nucleosomes within the cbh1 coding region under repressing conditions only. This indicates that CRE1 is important for correct nucleosome positioning within the cbh1 coding region under repressing conditions.