STUDIES TOWARDS THE X-RAY CRYSTAL STRUCTURE OF HELICASES. Christopher Putnam and John Tainer, The Scripps Research Institute, Molecular Biology, MB4, La Jolla, California 92037

DNA helicases are an important, structurally uncharacterized class of biological molecular motors that use the energy of nucleotide triphosphate hydrolysis to the unwinding of nucleic acid double helicies. The function of helicases in general are critical in the synthesis, maintence and repair of the genome of all organisms. The RuvB DNA helicase from Escherichia coli has been chosen as a starting point for investigation of this class of enzymes. RuvB is a relatively small DNA helicase that forms homohexamers around DNA. In vivo, the ATPase activity of RuvB is responsible for migration of Holliday junctions during genetic recombination. Preliminary diffraction data will be presented.