Sequence and Expression Analysis of the hrpB Pathogenicity Operon of Xanthomonas campestris pv. vesicatoria Which Encodes Eight Proteins with Similarity to Components of the Hrp, Ysc, Spa, and Fli Secretion Systems. Stefan Fenselau . Institut fur Genbiologische Forschung Berlin GmbH, 14195 Berlin, Germany. Ulla Bonas (2); (2) CNRS Institut des Sciences Vegetales, Avenue de la Terrasse, 91198 Gif-sur-Yvette, France. MPMI 8:845-854. Accepted 11 September 1995. Copyright 1995 The American Phytopathological Society.

In (his paper we describe the molecular characterization of hrpB, the largest operon in the Xanthomonas campestris pv. vesicatoria hrp cluster. The hrpB region encompasses 6 kb and encodes eight putative proteins, seven of which were expressed in Escherichia coli. The IIrpB3 protein is the only one carrying a signal peptide sequence at the N-terminus and is a putative lipoprotein localized in the outer membrane of X. campestris pv. vesicatoria. The HrpB4 and HrpB8 proteins contain one and five putative transmembrane domains, respectively, and arc most likely associated with the inner membrane. The HrpB3, HrpB5, HrpB6, and HrpB8 proteins show sequence similarity to putative components of different type III protein secretion pathways in bacteria. Examples include Hrp proteins from other plant pathogens, YscJ, YscN, YscL, and YscT of Yersinia spp., and MxiJ, Spa47, and Spa29 of Shigella flexneri. The transcription start site and the hrpB promoter was identified. The minimal hrpB promoter region of 90 bp contains a novel sequence motif, the PIP-box, which might play a role in transcription activation of the hrpB operon and possibly other plant-induced genes of X. campestris pv. vesicatoria