A large gene cluster for the Clostridium cellulovorans cellulosome

A large gene cluster for the Clostridium cellulovorans cellulosome has been cloned and sequenced upstream and downstream of the cbpA and exgS genes (C .-C. Liu and R. H. Doi, Gene 211:39-47, 1998). Gene walking revealed that t he engL gene cluster (Y. Tamaru and R H. Doi, J. Bacteriol. 182:244-247, 20 00) was located downstream of the cbpA-exgS genes. Further DNA sequencing r evealed that this cluster contains the genes for the scaffolding protein Cb pA, the exoglucanase ExgS, several endoglucanases of family 9, the mannanas e ManA and the hydrophobic protein HbpA containing a surface layer homology domain and a hydrophobic (or cohesin) domain. The sequence of the clustere d genes is cbpA,-exgS-engH-engK-hbpA-engL-manA-engM-engN and is about 22 kb in length. The engN gene did not have a complete catalytic domain, indicat ing that engN is a truncated gene. This large gene cluster is flanked at th e 5' end by a putative noncellulosomal operon consisting of nifV-orf1-sigX- regA and at the 3' end by noncellulosomal genes with homology to transposas e (trp) and malate permease (mle). Since gene clusters for the cellulosome are also found in C. cellulolyticum and C. josui, they seem to be typical o f mesophilic clostridia, indicating that the large gene clusters may arise from a common ancestor with some evolutionary modifications.