Crystal structure of a CAP-DNA complex: the DNA is bent by 90 degrees
Schultz, S. C.; Shields, G. C.; Steitz, T. A. Crystal Structure of a CAP-DNA Complex: The DNA Is Bent by 90 Degrees. Science 1991, 253 (5023), 1001-1007.
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.