The nagB gene encoding beta-N-acetylglucosaminidase from S. thermoviolaceus OPC-520 was cloned and sequenced. The nagB gene could encode a protein of 541 amino acids with a calculated molecular mass of 58274. NagB revealed significant similarities to beta-N-acetylhexosaminidases and chitobiases from bacteria, which are classified into family 20 glycosyl hydrolases. NagB effectively hydrolyzed all of the chitin oligosaccharides from dimer to hexamer. (C) 1998 Elsevier Science B.V. All rights reserved.