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Role of CRP in transcription activation at Escherichia coli lac promoter: CRP is dispensable after the formation of open complex

1995; Oxford University Press; Volume: 23; Issue: 4 Linguagem: Inglês

10.1093/nar/23.4.599

1362-4962

Hideaki Tagami, Hiroji Aiba,

Bacteriophages and microbial interactions

The role of cAMP receptor protein (CRP) in transcription activation at the Escherichla coil lac promoter was investigated focusing on the steps after the formation of open complex. Although CRP binding to the lac DNA is stabilized in the ternary open complex, a high concentration of heparin dissociates CRP from the open complex without affecting the interaction be tween RNA polymerase and promoter, resulting in a binary complex. The release of CAP is directly shown by Western blotting and DNase I footprlnting. The binary complex exhibits a siightiy increased gel mobility compared to the ternary complex. The binary complex retains the characteristics of the open com plex in footprinting pattern which is essentially ident ical with that of the open complex of the lac UV5 promoter. The binary compiex Is competent for tran scription. These results indicate that CAP is not necessary for the maintenance of active open com plex. in addition, the removal of CAP does not increase the production of abortive RNAs. We conclude that the contact between CRP and RNA poiymerase is not essential for transcription activation after the forma tion of the open complex at the lac promoter. In other words, the role of CRP in the lac promoter is restricted to the steps up to the formation of open complex.