Crystallization and preliminary X-ray investigation of the complex of RNase Sa with wild-type barstar.

RNase Sa, an extracellular ribonuclease produced by Streptomyces aureofaciens, is inhibited by barstar, the natural protein inhibitor of barnase, the ribonuclease of Bacillus amyloliquefaciens. The complex of RNase Sa with wild-type barstar was crystallized by hanging-drop vapour diffusion. It was shown by sodium dodecyl sulfate polyacrylamide gel electrophoresis that RNase Sa and barstar are present in equimolar proportions in the crystals. The crystals are in the hexagonal space group P65 with unit cell dimensions a = b = 56.95, c = 135.8 A. They diffract to 1.7 A resolution at the DESY synchronton source. The asymmetric unit contains one molecule of the complex.