MOLECULAR-CLONING AND EXPRESSION IN SACCHAROMYCES-CEREVISIAE OF 2 EXOCHITINASES FROM TRICHODERMA-HARZIANUM

The synthetic exochitinase substrate 4-methylumbelliferyl N-acetylgluc osamine was used to identify seven full-length exochitinase-encoding c DNAs from a Trichoderma harzianum cDNA library by expression in yeast. The cDNA clones represented transcripts of two exochitinase genes, de signated as exc1 and exc2, which cross-hybridized under moderate strin gency conditions in genomic Southern blots. The exc1 cDNA encodes a 57 8 amino acid polypeptide showing 72 % similarity to the exc2-encoded 6 02-residue polypeptide. The deduced exochitinase amino acid sequences were found to be homologous with mammalian and fungal hexosaminidases as well as a bacterial chitobiosidase. The substrate specificity of th e recombinant enzymes expressed in S. cerevisiae indicates that the en zymes are N-acetylglucosaminidases releasing single N-acetylglucosamin e residues from the non-reducing end of the chitin substrate.