The Phage 434 Cro / O , l Complex at 25 A Resolution

The crystal structure of phage 434 Cro protein in complex with a 20 base-pair D1VA fragment has been determined to 2.5 A resolution. The DNA fragment contains the sequence of the OR1 operator site. The structure shows a bent conformation for the DNA, straight,er at the center and more bent at the ends. The central base-pairs adopt conformations with significant deviations from coplanarity. The two molecules interact extensively along their common interface, both through hydrogen bonds and van der Waals interactions. The significance of these interactions for operator binding and recognition is discussed.