Use of a fusion protein to obtain crystals suitable for X-ray analysis: Crystallization of a GST-fused protein containing the DNA-binding domain of DNA replication-related element-binding factor, DREF

Crystals of glutathione-S-transferase (GST)-fused protein containing the DNA-binding domain of DNA replication-related element-binding factor, DREF, were obtained under crystallization conditions similar to those for GST. Preliminary X-ray crystallographic analysis revealed that crystals of the GST-fused protein belong to space group P6(1)22 or P6(5)22 with unit cell dimensions a = b = 140.4 Angstrom, c = 93.5 Angstrom and gamma = 120 degrees, having one molecule in the crystallographic asymmetric unit. The crystals diffract to 2.5 Angstrom resolution. The cell dimensions are related to those of GST crystals thus far reported. Crystallization of the DNA-binding domain that was cleaved from the fused protein by thrombin was also carried out using several methods under numerous conditions, but efforts to produce well-ordered large crystals were unsuccessful. A possible application of GST-fusion proteins for small target proteins or domains to obtain crystals suitable for X-ray structure determination is proposed.