A PRELIMINARY REFINEMENT OF YEAST tRNAPhe

The crystal structure of yeast t RNAPhe (in the orthorhombic form) is being refined at 3 A resolution in order to obtain a set of atomic coordinates that: (1) fit the X -ray diffraction data and (2) are consistent with the geometry of standard nucleotides and do nO"[ violate non-bonded interactions. Two directions are being taken to obtain the above goal. One is the 'real space refinement' procedure of Diamond pursued by the M.1. T. group and the other is the procedure which we have been developing at Duke University, which is described here. In the course of this refinement we have applied some crystallographic techniques that are not commonly used by macromolecular crystallographers, and have developed a convenient way to handle nucleic acid structures in a computer. It must be stressed at the outset that compared to the state of refinement achieved in some protein structures at high resolution (e.g., rubredoxin [1 J, high potential iron protein [2J, and the complex of bovine trypsin and bovine pancreatic trypsin inhibitor [3J), we are at a very early stage. Our present stage of refinement might be considered as model building guided by the electron density map.