Crystallization and X-ray diffraction studies of a 434 Cro-DNA complex.

Crystals have been obtained of the bacteriophage 434 Cro protein bound to a synthetic DNA operator. An analysis of the packing shows that the complexes stack end-to-end along crystallographic axis, forming long rods with non-crystallographic 11(3) screw symmetry. The average number of DNA base-pairs per turn is 10.27, which is somewhat more overwound as compared with the 434 repressor-DNA crystals of Anderson et al. Diffraction extends to 3 A along the rod direction and to 5 A in perpendicular directions.