Improved crystals of Thermus thermophilus prolyl-tRNA synthetase complexedwith cognate tRNA obtained by crystallization from precipitate

The complex between Thermus thermophilus prolyl-tRNA synthetase (ProRSTT) a nd its cognate tRNA has been crystallized using two different isoacceptors of tRNA(Pro). Similar bipyramidal crystals of the complexes of ProRSTT with the two different tRNA(Pro) isoacceptors grow within two weeks from 32% sa turated ammonium sulfate solution, They belong to space group P4(3)2(1)2, w ith unit-cell parameters a = 143.1, b = 143.1, c = 228.6 Angstrom. The crys tals diffract weakly to a maximum resolution of 3.1 Angstrom. Superior qual ity crystals were obtained by growing slowly from precipitate over 5-6 mont hs. These are of the same space group but have slightly altered unit-cell p arameters, a = 140.8, b = 140.8, c = 237.0 Angstrom. These crystals diffrac t more strongly to at least 2.8 Angstrom resolution and a complete data set to 2.85 Angstrom resolution has been collected from a single crystal. Comp arison of the packing in the two crystal forms shows that domain flexibilit y contributes to the presence of different crystal contacts in the two form s.