Temperature-inducible gene expression in Bacillus subtilis mediated by the cI857-encoded repressor of bacteriophage...

An efficient system to control the expression of cloned genes in Bacillus subtilis was established by introducing the Escherichia coli bacteriophage lambda cI857 repressor-pR promoter system into this host. A staphylokinase reporter gene (sak42D), which was fused to the lambda pR promoter was constitutively expressed in B. subtilis even when the cI857 gene was present on the same plasmid. S1 nuclease mapping of the transcription start point confirmed that the pR promoter was active in B. subtilis. Constitutive expression under pR-control in B. subtilis was, therefore, likely to result from a lack of repressor formation caused by the inefficiency of cI857 expression signals in the Gram+ host. This lack of repressor synthesis was overcome by fusing the cI857 gene to sak42D transcription and translation signals which have previously been shown to function efficiently in B. subtilis. Plasmids carrying the cI857 gene together with an alpha-amylase-encoding gene (amy) under pR-control mediated temperature-inducible amy expression at 37 degrees C and 42 degrees C. The high repression factor (greater than or equal to 1400) was comparable to the OR efficiencies reported in E. coli.