STRUCTURAL DIVERSITY IN FILAMENTOUS BACTERIOPHAGES. Makowski, L., Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306-3015, USA

X-ray and neutron diffraction data have been used to study the structure of filamentous bacteriophage M13 and Pf1, and chemically and genetically constructed variants of these particles. Ambiguity is intrinsic to the analysis of the structure of macromolecular assemblies using fiber diffraction. The ratio of data-to-model parameters for fiber diffraction is substantially lower than for x-ray crystallography. Even when the number of isomorphous derivatives are available, it may be not possible to obtain a unique structural solution from fiber diffraction data. Consequently, after a number of years, there continues to be substantial controversy in the literature about the filamentous bacteriophages M13 and Pf1. Differences among the molecular models for the viruses have substantial implications for our understanding of their membrane-mediated assembly, and for their use in phage display technology. It is now possible to obtain fiber diffraction data from a wide range of structural variants of filamentous bacteriophages that can provide rigorous tests of competing structural models. The relative positions and fidelity with which known structural features of the variants are reproduced in difference maps calculated on the basis of competing structural models provides a significant test of the competing models. The use of this strategy for exploring competing models of the coat proteins of filamentous bacteriophages Pf1 and M13 is demonstrated.