STRUCTURE OF RIBONUCLEASE-S AT 6 A RESOLUTION

The determination of the 3 dimensional structure of ribonuclease-S at a resolution of 6 A is described. The X-ray phase angle calculations are based on isomorphous and anomalous diffraction data for the protein and 3 heavy atom derivatives. At this low resolution, the binding of the nucleotide competitive inhibitor uridine 2[image],(3[image])-phosphate in the strong ammonium sulfate solution used to maintain the crystals does not cause any observable conformational change in the enzyme. The structure is generally compatible with the chain model for RNase-A proposed by Kartha, Bello, and Harker.