CRYSTALLIZATION AND PRELIMINARY-X-RAY DIFFRACTION ANALYSIS OF DOUBLE-HELICAL RNA OCTAMERS

Single crystals of a chemically synthesized self-complementary RNA oct amer with sequence r(CCCCGGGG) have been obtained by screening 50 diff erent conditions at room temperature using a standard sparse-matrix sa mpling method. Two crystal forms with different morphologies grew unde r diverse crystallization conditions within days by hanging-drop vapor diffusion. Hexagonal crystals with space group P6(1)22 (one strand pe r asymmetric unit) and unit-cell dimensions a = b = 39.73 and c = 58.5 5 Angstrom diffracted to 2.6 Angstrom. Rhombohedral crystals with spac e group R32 (one duplex per asymmetric unit) and unit-cell dimensions a=b=42.38 and c=131.70 Angstrom, (hexagonal setting) diffracted beyond 1.5 Angstrom. Data sets for both crystal forms were collected on imag e-plate/rotating-anode generator equipment and structure determination s and refinements are under way.