A new cellulase gene was cloned and expressed inEscherichia colifrom a thermophilic anaerobe, strain NA10. A 7.4 kbEcoRI fragment of NA10 DNA encoded the cellulase which hydrolyzed carboxymethyl cellulose, lichenan, andp-nitrophenyl-β-d-cellobioside, but could not digest laminarin andp-nitrophenyl-β-d-glucoside. The cloned enzyme could digest cellooligosaccharides and release cellobiose as a main product from cellotetraose but could not digest cellobiose. It was distinct from the endoglucanase which was cloned by us previously from NA10 strain in terms ofp-nitrophenyl-β-d-cellobioside degradation activity and the location of restriction enzyme sites. The enzyme produced byE. colitransformant was extremely heat-stable and the optimum temperature for the enzymatic reaction was 80°C. Fifty three percent of the cloned enzyme was detected in the periplasm and the remaining activity existed in the cellular fraction in theE. colitransform
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