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  • Title: Synergy between Escherichia coli CAP protein and RNA polymerase in the lac promoter open complex.
    Author: Straney DC, Straney SB, Crothers DM.
    Journal: J Mol Biol; 1989 Mar 05; 206(1):41-57. PubMed ID: 2649687.
    Abstract:
    Characterization of ternary complexes containing an Escherichia coli lac promoter DNA fragment, CAP protein and RNA polymerase, separated on non-denaturing polyacrylamide gels and footprinted in the gel slice, reveals a striking stabilization of CAP against dissociation in the open complex, compared to the CAP-DNA complex lacking RNA polymerase. The stabilization is lost when half a helical turn of DNA is inserted between CAP and polymerase sites, but is partially restored with an 11 base-pair insert; stimulation of transcription parallels the stabilization effect. This behavior suggests a direct protein-protein interaction. Comparison of initiation kinetics for wild-type and a mutant in which the P2 promoter has been inactivated shows that CAP both strengthens binding in the closed complex and accelerates isomerization to the open complex; the latter effect accounts for the bulk of the observed transcriptional activation.
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