| The structure of monoclinic crystal form of yeast phenylalanine tRNA has been redetermined by X-ray crystallography at 1.93 A resolution, which is significantly higher than that at which this landmark structure was originally determined more than 20 years ago. The structure of yeast tRNA phe described here is more accurate than its predecessors not only because it incorporates higher resolution data, but also because it has been refined using powerful techniques that were not available when its antecedents were published. In its general morphology, as expected, the 1.93 A resolution structure scarcely differs at all from its predecessors, but there are important differences in detail. In loop regions particularly, backbone torsion angles in the new structure differ substantially from those reported earlier. Several new divalent cation binding sites have been identified, and the water structure that has emerged is also different.;Elongation Factor G is a G-protein that catalyzes the translocation step in protein biosynthesis. Its third domain was cloned and overexpressed in E. coli and purified by column chromatographic methods. Circular Dichroism spectra of Domain III indicate that the domain forms secondary structures, and that its secondary structure is fairly stable. However, the presence of a great many overlapping cross-peaks in the domain's homonuclear and heteronuclear NMR spectra suggests that its tertiary structure is very flexible. The data suggest that the domain is about half structured and half disordered. This may explain why domain III is only poorly visible in the whole EFG crystal structure. |
