The gene encoding an endo-1,4-beta-glucanase from Ruminococcus albus F-40 was cloned in Escherichia coil JM109 using pBR322. The nucleotide sequence of the 1,798 bp PstI-PvuII fragment which includes a cellulase gene was determined. There was a single open reading frame (ORF) consisting of 936 bp encoding a peptide of 312 amino acid residues with a molecular weight of 35,766. The N-terminal amino acid sequence determined for the enzyme expressed in E. coli was identical to that deduced from the beginning of the ORF. A putative ribosome-binding site and a promoter were located upstream of the ORF. Activity was expressed from this fragment when it was subcloned in both orientations in pUC118 and pUC119, indicating that its own promoter functioned in E. coli. The amino acid sequence of the endoglucanase deduced from the nucleotide sequence showed 44% homology with CelA from Butyrivibrio fibrisolvens A46, suggesting that this enzyme was a member of family A2. The enzyme purified from E. coli exhibited the highest activity against carboxymethyl cellulose (CMC) at 40 degrees C and pH around 7.0.