X-ray Diffraction Study of a New Crystal Form of Yeast Phenylalanine tRNA

IN our continuing studies on the crystallography of tRNA¹ we have obtained a new crystal form of phenylalanine tRNA from baker's yeast. The crystals show particularly good stability to X-ray irradiation, lasting generally for about 100 h in the X-ray beam. Most importantly they produce reflexions which extend out to a resolution of about 3.0 Å. The crystals belong to the monoclinic system, space group P2i with two molecules of tRNA per unit cell (Table 1). Thus, there is only one molecule per asymmetric unit of structure. The unit cell dimensions (a=56.0, b=33.4, c=63.0 and β=90.9°) are the smallest yet reported for tRNA and place stringent constraints on the possible dimensions of the tRNA molecule.