Suppression of growth defects of α‐amylase secreting Escherichia coli by signal sequence fusion

Two fusions of the Bacillus stearothermophilusα‐amylase gene (amyS) with lacpoZ′ were constructed. The first, being a transcriptional fusion, placed amyS directly under lac promoter control eliminating interference by the endogenous promoter. IPTG induction of amyS transcription in this construction resulted in liberation of periplasmic proteins and eventually cell lysis. The other fusion replaced eight N‐terminal amino acid residues from the signal sequence by 11 residues from the lacZ′ moiety in pUC‐18. Translation initiation signals were also replaced by those from lacpoZ′. In this case IPTG induction resulted in secretion of approx. 35% of total α‐amylase activity in the growth medium after 24 h growth without detectable cell lysis.