VERNALIZATION1 (VRN1) is required in the model plant Arabidopsis thaliana for the epigenetic suppression of the floral repressor FLC by prolonged cold treatment. Stable suppression of FLC accelerates flowering, a physiological process known as vernalization. VRN1 is a 341-residue DNA-binding protein that contains two plant-specific B3 domains (B3a and B3b), a putative nuclear localization sequence (NLS) and two putative PEST domains. VRN1(208-341) includes the second B3 domain and a region upstream that is highly conserved in the VRN1 orthologues of other dicotyledonous plants. VRN1(208-341) was crystallized by the hanging-drop method in 0.05 M sodium acetate pH 6.0 containing 1.0 M NaCl and 18%(w/v) PEG 3350. Preliminary X-ray diffraction data analysis revealed that the VRN1(208-341) crystal diffracted to 2.1 A and belonged to space group C2, with unit-cell parameters a = 105.2, b = 47.9, c = 61.2 A, alpha = 90.0, beta = 115.4, gamma = 90.0 degrees . Assuming that two molecules occupy the asymmetric unit, a Matthews coefficient of 2.05 A(3) Da(-1) and a solvent content of 40.1% were calculated.