In glycerol-grown, but not in glucose-grown cultures, expression in TK24 of the cloned α-amylase gene () of is switched on toward the end of exponential growth. During this period, 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 -acting sequences involved in regulation. When this fragment was present on a multicopy plasmid, the growth-phase-dependent 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 expression in variants with deletions in the 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 expression partly growth-phase-independent, resistant to glucose repression, and insensitive to maltotriose induction.


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