Endo--1,4-glucanase genemcenA ofMicromonospora cellulolyticum 86W-16 was cloned, and the nucleotide sequence was determined. An open reading frame (ORF) of 1374 bases, coding for a peptide (McenA) of 457 amino acids and 46742 Da, was found. It is preceded by a Gram-positive type of ribosomebinding site and followed by an imperfect inverted repeat. A putative signal peptide containing 23 amino acids is at the N-terminus and a linker region possessing 37 amino acids is in the midpart of McenA. The N-half of McenA functions as the catalytic domain and the C-half might serve as a cellulosebinding domain (CBD). Deletion of the latter did not decrease the CMCase activity of McenA. Significant similarity (70%) was found between the amino acid sequences of McenA and MbcelA, an endoglucanase fromMicrobispora bispora.