, a low molecular-weight (14 kDa) hydrophilic protein, is a component of the P. syringae Hrp secretion machinery and is encoded by a conserved hrc gene (hrcQb). Based on the similarities of this secretion system with flagellar assemply, HrcQb
is assumed to be a structural protein of the basal body of the Hrp apparatus and is located in the cytoplasm as it homologous FliN?
The full length HrcQb protein is sensitive to proteolysis and had resisted all crystallization attempts. However, its C-terminal domain (the last 84 aa, hereafter referred as HrcQb-C) is stable and its structure has been determined by X-ray crystallography (pdb code 1o9y.pdb).