The genes for extracellular neutral protease (Npr) and intracellular serine protease (Isp) were cloned from Bacillus polymyxa in order to elucidate the process involved in the generation of multiple β-amylases and an α-amylase from a large amylase precursor. The npr gene was composed of 1,770 bp and 570 amino acids, while the isp gene was composed of 978 bp and 326 amino acids. Both proteases produced by E. coli cleaved the amylase precursor to generate β- and α-amylases. Furthermore, several other proteases produced the same products from the precursor. A 130-kDa amylase precursor has two large domain structures responsible for the generation of β- and α-amylases. The junction region of approximately 200 amino acids may be exposed on the surface of the molecule and susceptible to proteolytic enzymes, which results in the formation of multiple amylases.