Crystallization of the seryl‐tRNA synthetase: tRNAser complex of Escherichia coli

Crystals of the complex between seryl-tRNA synthetase and tRNA(2ser) from Escherichia coli have been obtained from ammonium sulphate solutions. The crystals are of the 1:2 enzyme:tRNA complex, belong to the space group C222(1), have cell dimensions of a = 128.9 A, b = 164.9 A, c = 127.3 A and diffract anisotropically from 3.5 to 4.5 A. An X-ray diffraction data set to 4 A has been collected. The combination of molecular replacement using the refined structure of the catalytic domain of the native enzyme, data from a heavy atom derivative and solvent flattening was used to produce a map at 4 A resolution. This shows that a tRNA molecule binds across the dimer, the anticodon stem and loop do not contact the protein and the helical arm of the enzyme contacts the T psi C loop and the long extra arm of the tRNA.