Molecular cloning and characterization of the beta-amylase gene from Bacillus circulans

A gene encoding the beta-amylase of Bacillus circulans was isolated from a lambda library and sequenced. The structural gene consists of a 1725 bp open reading frame encoding a polypeptide with a predicted molecular wt of 62830 Daltons. Two active forms of the enzyme were found when the gene was expressed in E. coli. The larger 60 kD form was approximately 3 kD larger than the mature beta-amylase secreted from B. circulans, suggesting that processing of this protein is different between the two species. The smaller 49 kD form is also present at a low level in B. circulans and may result from proteolytic cleavage. The enzyme has a temperature optimum of 50 degrees C. Two other genes, one encoding an alpha-amylase and one a pullulanase, were also isolated from the lambda library.