CRYSTALLIZATION OF ESCHERICHIA-COLI RUVA GIVES INSIGHTS INTO THE SYMMETRY OF A HOLLIDAY JUNCTION PROTEIN COMPLEX

The E. coli protein RuvA (resistance to ultraviolet light) has been ov erexpressed in E. coli, purified and crystallized using the hanging-dr op vapour-diffusion method with sodium chloride as the precipitant. Th e crystals, which diffract to beyond 1.9 Angstrom, belong to the tetra gonal system, space group P4 with unit-cell dimensions of a = 83.7, c = 33.1 Angstrom with a monomer in the asymmetric unit. RuvA is known t o be a tetramer and thus the crystal symmetry implies that its quatern ary structure will be based on fourfold rotation symmetry rather than 222 symmetry. This is consistent with electron microscopy data on Holl iday junction DNA complexes and implies that the arms of the four DNA duplexes involved in recombination adopt fourfold rotation symmetry.