CLONING AND EXPRESSION IN ESCHERICHIA-COLI OF A STREPTOMYCES BETA-GLUCOSIDASE GENE

Streptomyces A2 is a cellulolytic actinomycete isolated from the gut of termites. This microorganism secretes enzymes capable of degrading cellulose, which can be used as carbon source. A gene bank from Streptomyces A2 has been constructed in the Escherichia coli plasmid pUC 18 and screened for cellulase activities on agar plates. Two plasmids showing beta-glucosidase activity were isolated and characterized. The restriction map of the plasmids showed that both carried the same DNA fragment containing the beta-glucosidase gene. Transcription appeared to start from the plasmid lac promoter. The enzymatic activity was measured in cell extracts from E. coli cells carrying the plasmids. The length of the gene and the size of the coded protein were also determined.