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.