Interaction site of Escherichia coli cyclic AMP receptor protein on DNA of galactose operon promoters.

Abstract

Cyclic AMP (cAMP) and its receptor protein (CRP) have a dual role in the regulation of the 2 promoters that control the galactose (gal) operon of E. coli. One promoter, P1, requires cAMP.cntdot.CRP for activity; the other, P2 is inhibited by these factors. The interaction site of cAMP.cntdot.CRP on gal DNA was examined by using 3 types of protection experiments, involving DNase digestion and methylation by dimethyl sulfate. The results indicate that cAMP.cntdot.CRP binds to gal DNA in a segment located between 50 and 24 base pairs preceding the P1 start point for transcription. Although the location of the cAMP.cntdot.CRP interaction site is clearly different in gal and lac DNA, comparison of the DNA sequences suggests a similar recognition sequence. The location of the cAMP.cntdot.CRP-binding site in gal further suggests that protein-protein interactions between RNA polymerase and cAMP.cntdot.CRP play an important role in transcription initiation at the gal and possibly other cAMP-dependent promoters.