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Crystal structure of a CAP-DNA complex: the DNA is bent by 90 degrees

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Science  30 Aug 1991:
Vol. 253, Issue 5023, pp. 1001-1007
DOI: 10.1126/science.1653449


The 3 angstrom resolution crystal structure of the Escherichia coli catabolite gene activator protein (CAP) complexed with a 30-base pair DNA sequence shows that the DNA is bent by 90 degrees. This bend results almost entirely from two 40 degrees kinks that occur between TG/CA base pairs at positions 5 and 6 on each side of the dyad axis of the complex. DNA sequence discrimination by CAP derives both from sequence-dependent distortion of the DNA helix and from direct hydrogen-bonding interactions between three protein side chains and the exposed edges of three base pairs in the major groove of the DNA. The structure of this transcription factor--DNA complex provides insights into possible mechanisms of transcription activation.

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