NUCLEOTIDE-SEQUENCES OF THE CELB GENE ENCODING ENDO-1,4-BETA-GLUCANASE-2, ORF1 AND ORF2 FORMING A PUTATIVE CELLULASE GENE-CLUSTER OF CLOSTRIDIUM-JOSUI

The nucleotide sequence of the celB gene coding for endo-1,4-beta-gluc anase-2 (EG-2) of Clostridium josui was determined. The structural gen e consists of an open reading frame of 1,380 bp encoding a 460-amino a cid polypeptide. The deduced amino acid sequence of EG-2 shows high si milarities with the Clostridium cellulolyticum CelCCC (92.3%) and the Clostridium thermocellum endoglucanase CelA (61.6%) in the catalytic d omain, but no homology with EG-1 of C. josui. In the COOH-terminal reg ion of EG-2, there exists a reiterated segment similar to the segments present in many clostridial cellulases and hemicellulases. Upstream a nd downstream of the celB gene, two incomplete open reading frames (OR F1 and ORF2) were found to encode proteins homologous to the proteins which consist of the C. cellulolyticum cellulase gene cluster. ORF1 co ntaining a reiterated segment showed high similarities with the protei ns deduced from each ORF1 from C. cellulolyticum and Caldocellum sacch arolyticum. Downstream of the celB gene, ORF2 was found to encode a pr otein homologous to CelCCG of C. cellulolyticum and CelF of C. thermoc ellum. These results indicate that the celB gene, ORF1 and ORF2 formed a cellulase gene cluster strictly homologous to that of C. cellulolyt icum, which is proposed to be part of a single operon.