CRYSTALLIZATION AND PRELIMINARY-X-RAY INVESTIGATION OF 6 NEW CRYSTAL FORMS OF RIBONUCLEASE U-2 FROM USTILAGO-SPHAEROGENA

Ribonuclease (RNase) U-2 is a purine-specific endoribonuclease secrete d by Ustilago sphaerogena. In addition to type I and II crystals, six new crystal types of III, IV, V, VI, VII, and VIII have been obtained with the hanging-drop vapor-diffusion method. Type III and IV crystals were grown from ammonium sulfate solutions of pH 4.5. Type V is from an ammonium sulfate solution containing zinc chloride. Type VI is from a 2-methyl-2,4-pentanediol solution containing chloride. Type VII of a complex with adenosine-2'-monophosphate and type VIII of a complex w ith adenosine-3'-monophosphate are from polyethylene glycol 8000 solut ions containing calcium acetate. These types of crystals suggest polym orphic nature in crystallization of RNase U-2. Three-dimensional struc ture determinations of these new crystals are in progress, with the mo lecular replacement method by use of the structure of the type II crys tal.