Evidence for two functional gal promoters in intact Escherichia coli cells.

We have used an S1 mapping assay to demonstrate that the mRNA transcripts of the Escherichia coli galactose operon found in intact E. coli cells with a defect in adenylate cyclase or the cyclic AMP receptor protein contain at their 5' end about five nucleotides more than the gal mRNA molecules made in wild type cells. The same difference between gal RNA synthesized in vitro in the absence of cyclic AMP or cyclic AMP receptor protein and gal RNA made in the presence of these factors is detected by this assay. Our results strongly suggest that the same two overlapping promoters, which we previously identified by in vitro transcription of gal DNA fragments, also control the expression of the galactose operon in intact cells. The intracellular levels of cyclic AMP determine which promoter is utilized.