Synchrotron radiation as a tool for investigating virus structures

The smallest spherical viruses have a diameter of at least 200 AÊ [e.g. satellite tobacco necrosis virus (Liljas et al., 1982) and satellite tobacco mosaic virus (Larson et al., 1993)]. Many spherical viruses, such as southern bean mosaic virus (Abad-Zapatero et al., 1980) or rhinoviruses (Rossmann et al., 1985), have diameters of 300 AÊ , and many other viruses have much larger diameters [e.g. bluetongue virus (Grimes et al., 1998)], with iridiviruses (Van Etten et al., 1991) having diameters of as much as 2000 AÊ . Because of their spherical shape, these viruses are usually fairly easy to crystallize but, because of their size, the resolution, indexing and intensity measurements of the individual Bragg re ̄ections create severe experimental problems. Fortunately, the use of synchrotron radiation (Figs. 1 and 2) has made it possible to solve these problems in most cases.