REOVIRUS CORES: PROGRESS TOWARD A STRUCTURE. Karin M. Reinisch^*, Max L. Nibert⁺, Stephen C. Harrison^{*, *}Department of Molecular and Cellular Biology and Howard Hughes Medical Institute, Harvard University, Cambridge, MA 02l38,⁺Department of Biochemistry and Institute for Molecular Virology, University of Wisconsin-Madison, Madison, WI 53706

We will describe our progress toward a structure determination for cores of reovirus. Reovirus consists of a segmented ds RNA genome surrounded by two concentric protein shells. When the outer shell of reovirus is proteolytically removed, the viral core becomes active as a RNA processing machine. Cores of a strain T3D reassortant have been crystallized in spacegroup F432, a=1250Å. Crystals at cryogenic temperatures diffract to 6Å at the F1 beam line at CHESS. Our efforts at data collection and phasing will be described.