cDNA Cloning of a Trichoderma reesei Cellulase and Demonstration of Endoglucanase Activity by Expression in Yeast

Abstract

A Trichoderma reesei cDNA encoding a previously unknown protein with a C‐terminal cellulosebinding domain was obtained by complementation screening of a T. reesei cDNA library in a sec1 yeast mutant impaired in protein secretion. The T. reesei protein shows amino acid similarity over its entire length to the Agaricus bisporusi cellulose‐induced protein CEL1 whose function is not known. These two proteins form a new glycosyl hydrolase family, number 61. Expression of the T. reesei cDNA in yeast showed that it encoded a protein with endoglucanase activity and thus the protein was named EGIV and the corresponding gene eg14. Polyclonal antibodies were prepared against EGIV produced in Escherichia coli and detected a 56‐kDa protein in the T. reesei culture supernatant. Northern hybridisation revealed that T. reesei egl4 is regulated in the same manner as other cellulase genes of this fungus.