CRYSTAL-STRUCTURE OF AN IHF-DNA COMPLEX - A PROTEIN-INDUCED DNA U-TURN

Integration host factor (IHF) is a small heterodimeric protein that sp ecifically binds to DNA and functions as an architectural factor in ma ny cellular processes in prokaryotes. Here, we report the crystal stru cture of IHF complexed with 35 bp of DNA. The DNA is wrapped around th e protein and bent by >160 degrees, thus reversing the direction of th e helix axis within a very short distance. Much of the bending occurs at two large kinks where the base stacking is interrupted by intercala tion of a proline residue. IHF contacts the DNA exclusively via the ph osphodiester backbone and the minor groove and relies heavily on indir ect readout to recognize its binding sequence. One such readout involv es a six-base A tract, providing evidence for the importance of a narr ow minor groove.