Regulatory characteristics and promoter analysis of csiE, a stationary phase‐inducible gene under the control of σS and the cAMP—CRP complex in Escherichia coli

Sigma‐S and the cAMP—CRP complex are global regulatory factors involved in stationary‐phase induction of large groups of genes in Escherichia coli. csiE, a gene located at 57.25 min (co‐ordinate 2674) of the physical map of the E. coli chromosome, is under the control of both of these factors. Sigma‐S plays a positive, though not absolutely essential, role in the expression of csiE. Regulation by cAMP—CRP has both positive and negative elements, with the latter being dependent on the presence of σS, whose expression is negatively influenced by cAMP—CRP. csiE has a single transcriptional start site located 33 bp upstream of the initiation codon. By a 5′‐deletion approach, we show that 72 bp upstream of the csiE transcriptional start site are sufficient for regulation by σS and cAMP—CRP. A deletion upstream of nucleotide −38 with respect to the start site eliminates positive cAMP—CRP control and makes the remaining expression fully dependent on σS. Our results indicate that transcription at the csiE promoter can be initiated in vivo by σS‐containing RNA polymerase alone as well as by σ70‐containing RNA polymerase in conjunction with cAMP—CRP or a cAMP—CRP‐dependent secondary regulator. The promoter region of poxB, the structural gene for pyruvate oxidase, which is also under the control of σS and cAMP—CRP, is very similar to the corresponding region of csiE, suggesting a similar regulatory mechanism also for poxB.