DIFFERENT INDUCIBILITY OF EXPRESSION OF THE 2 XYLANASE GENES XYN1 ANDXYN2 IN TRICHODERMA-REESEI

Regulation of formation of the extracellular xylanase system of Tricho derma reesei QM 9414 during growth on xylan, cellulose, and replacemen t onto a number of soluble inducers was investigated by Northern analy sis of xyn1 and xyn2 transcripts and by the use of the Escherichia col i hph (hygromycin B-phosphotransferase-encoding) gene as a reporter. W hereas the xyn1 promoter is active in the presence of xylan and xylose , and virtually silenced in the presence of glucose, the xyn2 promoter enables basal transcription at a low level, but is enhanced in the pr esence of xylan and xylobiose and also of sophorose or cellobiose. The respective regulatory nucleotide regions were localized on a 221-base pair fragment and a 55-base pair fragment of the xyn1 and zyn2 5'-ups tream noncoding sequences, respectively. Electrophoretic mobility shif t assays, using cell-free extracts, identified induction-specific prot ein-DNA complexes: one complex of high mobility was observed under bas al, noninduced conditions (glucose) with xyn2, which was in part repla ced by a slow-migrating complex upon induction by xylan or sophorose. Both complexes bound to a CCAAT box. With xyn1, the induced complex al so binds to a CCAAT box, but this binding is not observed in the prese nce of the carbon catabolite repressor Cre1, which binds to a nearby l ocated consensus motif.