Metazoan cellulase genes from termites: intron/exon structures and sites of expression

Endogenous endo-beta-1,4-glucanase (EGase, EC 3.2.1.4) cDNAs were cloned fr om representatives of the termite families Termitidae and Rhinotermitidae. These EGases are all composed of 448 amino acids and belong to glycosyl hyd rolase family 9 (GHF9), sharing high levels of identity (40-52%) with selec ted bacterial, mycetozoan and plant EGases, Like most plant EGases, they co nsist of a single catalytic domain, lacking the ancillary domains found in most microbial cellulases. Using a PCR-based strategy, the entire sequence of the coding region of NtEG, a gene putatively encoding an EGase from Nasu titermes takasngoensis (Termitidae), was determined. NtEG consists of 10 ex ons interrupted by 9 introns and contains typical eukaryotic promoter eleme nts. Genomic fragments of EGase genes from Reticulitermes speratus (Rhinote rmitidae) were also sequenced. In situ hybridization of N. takasagoensis gu ts with an antisense NtEG RNA probe demonstrated that expression occurs in the midgut, which contrasts to EGase expression being detected only in the salivary glands of R. speratus. NtEG, when expressed in Escherichia coli, w as shown to have in vitro activity against carboxymethylcellulose. (C) 1999 Elsevier Science B.V. All rights reserved.