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Proc Natl Acad Sci U S A. 2009 Nov 24;106(47):19830-5. doi: 10.1073/pnas.0908782106. Epub 2009 Nov 10.

Three-dimensional EM structure of an intact activator-dependent transcription initiation complex.

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  • 1Department of Chemistry and Chemical Biology, Rutgers University, 610 Taylor Road, Piscataway, NJ 08854, USA.

Abstract

We present the experimentally determined 3D structure of an intact activator-dependent transcription initiation complex comprising the Escherichia coli catabolite activator protein (CAP), RNA polymerase holoenzyme (RNAP), and a DNA fragment containing positions -78 to +20 of a Class I CAP-dependent promoter with a CAP site at position -61.5 and a premelted transcription bubble. A 20-A electron microscopy reconstruction was obtained by iterative projection-based matching of single particles visualized in carbon-sandwich negative stain and was fitted using atomic coordinate sets for CAP, RNAP, and DNA. The structure defines the organization of a Class I CAP-RNAP-promoter complex and supports previously proposed interactions of CAP with RNAP alpha subunit C-terminal domain (alphaCTD), interactions of alphaCTD with sigma(70) region 4, interactions of CAP and RNAP with promoter DNA, and phased-DNA-bend-dependent partial wrapping of DNA around the complex. The structure also reveals the positions and shapes of species-specific domains within the RNAP beta', beta, and sigma(70) subunits.

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