CarbonSource Control ofCellobiohydrolas e IandII Formation byTrichoderma reesei

Regulation oftheformation andsecretion oftwocellulase components fromTrichoderma reesei QM 9414, cellobiohydrolases IandII(CBHIandCBHH,respectively), bythecarbon source wasinvestigated. With monoclonal antibodies against CBHIandCBHIIitwasfound that during cultivation oncarbon sources which enable fast growth (glucose, glycerol, andfructose), noformation ofCBH Ioccurred, whereas lowlevels of CBHIIwereformed. Lactose andcellulose, whichallow comparably slower growth, promoted theformation ofbothCBHIandCBHII.However, noncarbohydrate carbon sources ascitrate oracetate, whichalso enable onlyslowgrowth, didnotpromote theformation ofCBHIorCBHII.Theaddition ofglucose orglycerol to lactose- orcellulose-pregrown mycelia, ontheother hand, only partially reduced theformation ofCBHI.This reduction wasalso achieved byseveral other metabolizable andnonmetabolizable carbon compounds, e.g., fructose, galactose, j-methylglucoside, 2-deoxyglucose, andrhamnose, aswellasbytransfer tonocarbon source atall. Thisresult indicates that thecontrol ofCBHIsynthesis bythecarbon source isduetoinduction andnottorepression. Theuseofcycloheximide and5-fluorouracil asinhibitors atandbefore translation, respectively, revealed ahalf-life forCBHImRNAofatleast several hours, whichmay,atleast inpart, account fortheprolonged synthesis ofsomeCBH Iunderthese conditions. Northern (RNA)hybridization withfull copies ofcbhlandcbh2genes indicated that thecontrol ofCBHIandCBHIIbiosyntheses bythecarbon source operates mainly atthepretranslational level. Weconclude that thelowrate ofcellulase synthesis onglucose and someother carbon sources isduetothelackofaninducer andnottocarbon source repression.