A cDNA expression library of the rumen fungus was made in . Cellulolytic clones were identified by screening on a medium containing carboxymethylcellulose. Restriction mapping and Southern hybridization analysis of selected clones revealed three distinct cellulase cDNAs, designated , and . Studies on the substrate specificity showed that the enzyme encoded by had high activity towards amorphous and microcrystalline cellulose, while the and enzymes had relatively high activity on carboxymethylcellulose, with little activity on microcrystalline cellulose. Analysis of hydrolysis products from defined cellodextrins showed that the and enzymes hydrolysed β-1,4-glucosidic linkages randomly, whereas the enzyme cleaved cellotetraose to cellobiose, and cellopentaose to cellobiose and cellotriose. Cellobiose was also the only product detectable from hydrolysis of microcrystalline cellulose by the enzyme. Based on substrate specificity and catalytic mode, appears to encode a cellobiohydrolase, while and encode endoglucanases. Northern blot hybridization analysis showed that expression of the three cellulase transcripts in was induced by cellulose.


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