Cloning, characterization and regulation of an alpha-amylase gene from Streptomyces limosus.

An alpha-amylase gene (aml) of Streptomyces limosus ATCC 19778 was cloned in Streptomyces lividans 66. S1 mapping experiments identified an aml transcript 1.8 kb in length and the extracellular enzyme was estimated to be 59 kD in size, suggesting that aml was transcribed as a monocistronic mRNA species. Expression of the gene was induced by maltose (or maltodextrins) in S. limosus and when aml was cloned in S. lividans or Streptomyces coelicolor A3(2). In S. limosus, mannitol repressed aml expression while glucose had little or no effect; in S. lividans and S. coelicolor the relative effects of the two sugars were reversed. Both induction and carbon-source repression of aml expression appeared to occur at the level of transcriptional initiation. Glucose repression in S. coelicolor was dependent upon a functional glucose kinase gene.