DNA Sequences of Three beta-1,4-Endoglucanase Genes from Thermomonospora fusca

摘要

An important step toward understanding the mechanism of action of an enzyme isthe determination of its amino acid sequence. In recent years, this usually has been done by determining the DNA sequence of the structural gene that encodes the protein, as DNA sequencing is simpler and more precise than protein sequencing. The sequences of a number of cellulase genes have been determined, and this work has be reviewed by Beguin et al. We have been studying the cellulases of a thermophilic, filamentous soil bacterium, Thermomonospora fusca, and have purified five antigenically distinct cellulases, designated E1 to E5, from the culture supernatant of an extracellular-protease-negative mutant of T. fusca (34). All five enzymes are beta-1,4-endoglucanases, but they show considerable variation in their specific activities on several substrates and in their physical properties. The enzymes from T. fusca are heat stable and active over a broad pH range with an optimum centered at pH 6.5.