Macromolecular crystallography with synchrotron radiation: collection and processing of data from crystals with a very large unit cell

Hexagonal crystals of cowpea mosaic virus in space group P6₁22 (or its enantiomorph) with a = 451 and c = 1038 Å have been analyzed using the synchrotron X-ray source at LURE. Data were collected using an X-ray beam of size 0.18 × 0.22 mm permitting resolution of reflections along the c* direction. The beam was defined using a multiple slit system at both the monochromator and at the collimator. A helium path was used to reduce air scatter as a specimen-to-film distance of 175 mm was employed. Data to 4.3 Å resolution were recorded on each film. The films were processed to 6 Å resolution using the oscillation photograph processing package developed by Rossmann [J. Appl. Cryst. (1979), 12, 225-238] with minor modifications to the normal procedures. One film was processed to 4.3 Å resolution establishing the feasibility of intermediate resolution analysis. Statistical analysis of the processed data showed excellent correlation between symmetry-equivalent reflections. Post refinement of oscillation angles and lattice constants was very stable and led to significantly improved scaling of partially recorded reflections.