The role of purification in the crystallization of proteins and nucleic acids
Abstract In structural biology, the crystallization of the macromolecules often represents the most challenging step. Beside classical factors which determine the solubility of macromolecules, purity of compounds is another major parameter governing crystal growth. With aminoacyl-tRNA synthetases and transfer ribonucleic acids as examples, it will be shown that molecules to be crystallized not only have to be pure in terms of contaminating molecules, but also in terms of sequence integrity and conformational homogeneity. A chromatographic method based on salting-out of proteins or nucleic acids on Sepharose 4B gels and back-solubilization with inverse salt gradients will be discussed in the light of crystal growth experiments.