HutP is an RNA-binding protein and regulates the expression of the histidine utilization (hut) operon in Bacillus subtilis by binding to cis-acting regulatory sequences on hut mRNA. HutP and its mutant, which has increased affinity for the regulatory sequences, were purified and crystallized by the hanging-drop vapor diffusion method. The space group was P2(1)3 with unit cell dimensions a = b = c = 95.6Angstrom for HutP and a = b = c = 96.8Angstrom for the mutant. Complete data sets of 3.0-Angstrom resolution for wild-type HutP and of 2.70-Angstrom resolution for the mutant HutP were collected. (C) 2002 Elsevier Science (USA). All rights reserved.