Molecular Cloning and Structure of the Streptomyces hygroscopicus α-Amylase Gene

We have isolated and sequenced a gene (amy) coding for α-amylase [EC. 3.2.1.1] from the Streptomyces hygroscopicus genome. Subcloning experiments indicated that amy could be expressed from the lac promoter in E. coli or its own promoter in S. lividans. The amy nucleotide sequence indicated that it coded for a protein of 52 kilodaltons (478 amino acids). The conserved amino acid sequences of other α-amylase were found in three separate regions of the S. hygroscopicus α-amylase. The 30-residue leader sequence showed similarities to those found in other prokaryotes. The DNA sequence 5′ to the amy structural gene contained a sequence complementary to the 3′-terminal sequence of 16S rRNA of S. lividans. The transcriptional start points of amy were determined, but the promoter of amy was not similar to the consensus sequence found in other prokaryotes. The recombinant strain, S. hygroscopicus containing amy on a high copy plasmid, produced α-amylase 4 times excess than the host strain.