MOLECULAR-CLONING, NUCLEOTIDE SEQUENCING, AND EXPRESSION OF THE BACILLUS-SUBTILIS (NATTO) IAM1212 ALPHA-AMYLASE GENE, WHICH ENCODES AN ALPHA-AMYLASE STRUCTURALLY SIMILAR TO BUT ENZYMATICALLY DISTINCT FROM THAT OF BACILLUS-SUBTILIS 2633

An α-amylase gene of Bacillus subtilis (natto) IAM1212 was cloned in a λEMBL3 bacteriophage vector, and the nucleotide sequence was determined. An open reading frame encoding the α-amylase (AMY1212) consists of 1,431 base pairs and contains 477 amino acid residues, which is the same in size as the α-amylase (AMY2633) of B. subtilis 2633, an α-amylase-hyperproducing strain, and smaller than that of B. subtilis 168, Marburg strain. The amino acid sequence of AMY1212 is different from that of AMY2633 at five residues. Enzymatic properties of these two α-amylases were examined by introducing the cloned genes into an α-amylase-deficient strain, B. subtilis M15. It was revealed that products of soluble starch hydrolyzed by AMY1212 are maltose and maltotriose, while those of AMY2633 are glucose and maltose. From the detailed analyses with oligosaccharides as substrates, it was concluded that the difference in hydrolysis products of the two similar α-amylases should be ascribed to the different activity hydrolyzing low-molecular-weight substrates, especially maltotriose; AMY1212 slowly hydrolyzes maltotetraose and cannot hydrolyze maltotriose, while AMY2633 efficiently hydrolyzes maltotetraose and maltotriose. Further analyses with chimeric α-amylase molecules constructed from the cloned genes revealed that only one amino acid substitution is responsible for the differences in hydrolysis products.