Crystallization and preliminary X-ray crystallographic analysis of sterol transcription factor Upc2 from Saccharomyces cerevisiae.

Upc2, a zinc-cluster transcription factor, is a regulator of ergosterol biosynthesis in yeast. In response to sterol levels, the transcriptional activity of Upc2 is controlled by the C-terminal domain. In this study, the C-terminal regulatory domain of Upc2 from Saccharomyces cerevisiae was purified and crystallized by the vapour-diffusion method. To improve the diffraction quality of Upc2 crystals, a Upc2 fusion protein in which 11 residues of the variable loop (residues 715-725) were replaced by T4 lysozymes in Upc2 (Upc2-T4L) was engineered. The Upc2-T4L crystals diffracted to 2.9 Å resolution using synchrotron radiation. The crystal was trigonal, belonging to space group P3(2) with unit-cell parameters a = 67.2, b = 67.2, c = 257.5 Å. The Matthews coefficient was determined to be 3.41 Å(3) Da(-1) with two molecules in the asymmetric unit. Initial attempts to solve the structure by the single-anomalous dispersion technique using selenomethionine were successful.