Sequences involved in growth-phase-dependent expression and glucose repression of a Streptomyces α-amylase gene

In glycerol-grown, but not in glucose-grown cultures, expression in Streptomyces lividans TK24 of the cloned α-amylase gene (aml) of Streptomyces limosus is switched on toward the end of exponential growth. During this period, aml expression is further inducible by maltotriose. We showed that a 378 bp fragment, extending from position −204 through to + 174 (relative to the transcriptional start site), included cis-acting sequences involved in aml regulation. When this fragment was present on a multicopy plasmid, the growth-phase-dependent aml expression conferred by a DNA fragment cloned on a compatible low-copy-number plasmid was greatly enhanced, as if negative regulators were being titrated. A study of the regulation of aml expression in variants with deletions in the aml promoter region indicated that a direct repeat (DR) between positions −124 and −106 (relative to the transcriptional start site) and an inverted repeat (IR) between positions +9 and +24 were good candidates for secondary and primary operator sites, respectively. Deletion of a 29 bp fragment containing the IR rendered aml expression partly growth-phase-independent, resistant to glucose repression, and insensitive to maltotriose induction.