Large-scale purification and crystallization of the endoribonuclease XendoU: troubleshooting with His-tagged proteins

Recombinant His-tagged XendoU, a eukaryotic endoribonuclease, appeared to aggregate in the presence of divalent cations. Monodisperse protein which yielded crystals diffracting to 2.2 Å was obtained by addition of EDTA.