Phytoreovirus T=1 core plays critical roles in organizing the outer capsidof T=13 quasi-equivalence

The structures of the double-shelled rice dwarf virus and of its single-she ll core have been determined by cryoelectron microscopy and image reconstru ction. The core carries a prominent density located at each of the icosahed ral faces of its T = 1 lattice. These protrusions are formed by outer shell trimers, tightly inserted at the threefold positions of the core. Such con figuration of the core may guide the assembly of the outer shell, aided by lateral interactions between its subunits, into a T = 13 lattice. The organ ization of the phytoreovirus capsid elucidates for the first time a general model for assembling two unique T numbers of quasi-equivalence. (C) 2000 A cademic Press.