Crystallization of the MS2 translational repressor alone and complexed to bromouridine.

The coat protein from the MS2 bacteriophage plays a dual role by encapsidating viral RNA and also by binding RNA as a translational repressor. In order to study the isolated dimer in a conformation not influenced by capsid interactions, a mutant molecule was crystallized that is defective in capsid assembly but is an active repressor. The unassembled dimer crystallized in the space group P21212 with a = 76.2, b = 55.7, and c = 28.4 A. In these crystals, monomers were related by twofold symmetry. When this dimer was co-crystallized with 5-bromouridine, crystals formed in space group R3 with a = b = 155.9 A, c = 29.9 A, gamma = 120 degrees; the dimer was the asymmetric unit.