Bluetongue virus: the role of synchrotron radiation

The determination of the structure of the transcriptionally active core par ticle of bluetongue virus is discussed. This particle is approximately 700 Angstrom in diameter and reasonably well ordered, but fragile, crystals hav e been obtained from two different serotypes of the virus. Cryocrystallogra phy proved difficult and a large number of crystals were analysed at room t emperature to accumulate a reasonably complete data set. The effects of syn chrotron optics, station design and detector on the signal-to-noise for the se weak data are discussed, with particular reference to station ID2 at the European Synchrotron Radiation Facility. Once the data had been gathered, structure determination was straightforward, using a model derived from a c ombination of electron microscopy and protein crystallography to obtain ini tial phases. Despite apparent isomorphism, it is suspected that the crystal lattice 'ages', perhaps reflecting both the inevitable weakness of the for ces holding crystals of such a large macromolecular complex together and fl exibility in the particle.