초록
<P><B>Background</B></P><P><I>Trichoderma reesei</I> represents an important workhorse for industrial production of cellulases as well as other proteins. The large-scale production is usually performed in a substrate-inducing manner achieved by a fine-tuned cooperation of a suite of transcription factors. Their production and subsequent analysis are, however, often either difficult to manipulate or complicated by the concomitant production of other inducible proteins. Alternatives to control gene expression independent of the nutritional state are thus preferred in some cases to facilitate not only biochemical studies of proteins but also genetic engineering of the producer.</P><P><B>Results</B></P><P>We identified a copper transporter encoding gene <I>tcu1</I> (jgi:Trire2:52315) in <I>T. reesei</I>, the transcription of which was highly responsive to copper availability. Whereas excess copper repressed the expression of <I>tcu1</I> from <I>T. reesei</I>, eliminating copper addition in the medium resulted in a high-level transcription of <I>tcu1</I>. The usefulness of the system was further illustrated by the high-level expression of specific cellulases driven by the <I>tcu1</I> promoter in <I>T. reesei</I> when cultivated on D-glucose or glycerol as the sole carbon source. A recombinant <I>T. reesei</I> strain, which overexpressed the main transcription activator of hydrolases (xylanase regulator 1) under the control of <I>tcu1</I> promoter, was found to be relieved from the carbon catabolite repression and thus displayed a constitutive cellulase expression. Moreover, the amount and activities of cellulases produced by this strain on glycerol or glucose fully recapitulated those of the parental strain produced on Avicel.</P><P><B>Conclusion</B></P><P>Expression of <I>T. reesei tcu1</I> gene was tightly controlled by copper availability, and a homologous protein expression system was developed based on this promoter. Deregulation of XYR1 (xylanase regulator 1) mediated by the <I>tcu1</I> promoter not only overcame the carbon catabolite repression of cellulases but also resulted in their full expression even on the non-inducing carbon sources.</P>