Xanthomonas axonopodis pv. citri YaeQ (XAC2396) is a member of a family of bacterial proteins conserved in several Gram-negative pathogens. Here, the cloning, expression, purification and crystallization of the 182-residue (20.6 kDa) YaeQ protein are described. Recombinant YaeQ containing selenomethionine was crystallized in space group P2(1) and crystals diffracted to 1.9 A resolution at a synchrotron source. The unit-cell parameters are a = 39.75, b = 91.88, c = 48.03 A, beta = 108.37 degrees. The calculated Matthews coefficient suggests the presence of two YaeQ molecules in the asymmetric unit. Initial experimental phases were calculated by the multiple-wavelength anomalous dispersion technique and an interpretable electron-density map was obtained.