CRYSTALLIZATION AND PRELIMINARY-X-RAY INVESTIGATION OF THE COMPLEX OFRNASE SA WITH WILD-TYPE BARSTAR

RNase Sa, an extracellular ribonuclease produced by Streptomyces aureo faciens, is inhibited by barstar, the natural protein inhibitor of bar nase, the ribonuclease of Bacillus amyloliquefaciens. The complex of R Nase 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 pro portions in the crystals. The crystals are in the hexagonal space grou p P6(5) with unit-cell dimensions a = b = 56.95, c = 135.8 Angstrom. T hey diffract to 1.7 Angstrom resolution at the DESY synchrotron source . The asymmetric unit contains one molecule of the complex.