TRIGGERING OF CELLULASE BIOSYNTHESIS BY CELLULOSE IN TRICHODERMA-REESEI - INVOLVEMENT OF A CONSTITUTIVE, SOPHOROSE-INDUCIBLE, GLUCOSE-INHIBITED BETA-DIGLUCOSIDE PERMEASE

We prepared [U-C-14]cellobiose by cultivating Acetobacter pasteurianus in the presence of [U-C-14]glucose and hydrolyzing the [U-C-14]cellul ose formed with beta-glucosidase-free cellulase from Trichoderma reese i. This C-14-labeled cellobiose was used to investigate the presence o f an uptake system for cellobiose in T. reesei. Evidence was obtained for the presence of a high affinity (K(m) for cellobiose 0.3 muM) but low activity (2.5 milliunits/mg fungal dry weight) cellobiose permease . The permease is formed constitutively, but higher levels are formed after addition of sophorose (glucosyl-beta-1,2-diglucoside), a reputed cellulase inducer. The permease appears to be specific for beta-diglu cosides, as the uptake of [U-C-14]cellobiose is inhibited by sophorose , gentiobiose (glucosyl-,beta-1,3-glucoside), and cellobiose. Under th ese conditions, cellooligodextrines (n, 4-7; final concentration, 1 mM ) are not inhibitors. Glucose, but no other monosaccharides, inhibits the permease. The hypersecretory mutant T. reesei RUT C-30 exhibits el evated permease activities, whereas in T. reesei QM 9979, a mutant str ain defective in the induction of cellulases by cellulose or sophorose , strongly reduced permease activities were demonstrated. The results stress a hitherto not recognized point of control in the induction of cellulases by T. reesei at the level of uptake of cellulose oligosacch arides.