The structures of a number of helical plant viruses will be determined at resolutions sufficient to describe the intact viruses in molecular detail, using the fiber diffraction methods already used successfully in this laboratory for tobacco mosaic virus (TMV) and the U2 strain of TMV. The viruses to be studied include viruses distantly related to TMV (cucumber green mottle mosaic virus and ribgrass mosaic virus), and the unrelated potexvirus papaya mosaic virus (PMV). The structure of the isolated coat protein of PMV will be determined crystallographically. Mutants of TMV, predicted from the structure to be deficient in assembly or disassembly, will be designed here and made by collaborators. Their assembly and disassembly properties will be studied here by electron microscopy and other measurements. Structures of mutants showing significantly changed assembly properties will be determined. %%% These rod-shaped viruses are the only viruses in which the entire nucleic acid genome can be seen using x-ray diffraction methods. Studies of their structures are important to understanding protein-nucleic acid interactions and the processes of molecular assembly and recognition in biological systems. Assembly and recognition are essential steps in many cellular processes, as well as in the processes of viral infection and propagation. The studies proposed here are therefore relevant to a wide variety of cellular systems of both medical and agricultural importance.
