Cloning and Characterization of tek, the Gene Encoding the Major Extracellular Protein of Pseudomonas solanacearum. Timothy P. Denny. Department of Plant Pathology, University of Georgia, Athens 30602 U.S.A. Lilia M. Ganova-Raeva (1), Jianzhong Huang (2), and Mark A. Schell (1,2). (1) Department of Plant Pathology and (2) Department of Microbiology, University of Georgia, Athens 30602 U.S.A. MPMI 9:272-281. Accepted 15 February 1996. Copyright 1996 The American Phytopathological Society.

Susceptiblc plants infected by Pseudomonas solanacearum usually wilt, largely due to extracellular proteins (EXPs) and the high-molecular-mass extracellular polysaccharide (EPS I) this pathogen produces. Circumstantial evidence suggested that a 28-kDa protein, the single most abundant EXP made by P. solanacearum in culture, is associated with production of EPS I, and thus might have a role in pathogenesis. The 28-kDa EXP was purified and, based on its N-terminal amino acid sequence, an oligonucleotide mixture was made and used as a hybridization probe to clone the gene encoding it. DNA sequence analysis suggested that the coding sequence for the 28-kDa EXP is within a gene, designated tek, that encodes a 58-kDa membrane-associated precursor protein that is processed by signal peptidase II during export. Analysis of radiola-beled polypeptides expressed from tek confirmed that it encodes a 58-kDa precursor protein, which is exported out of the cells as a 55-kDa preprotein and processed extracel-lularly to release the very basic 28-kDa EXP from its C terminus. The position, transcriptional direction, and regulated expression of tek suggest that it is cotranscribed with xpsR, a gene essential for regulating biosynthesis of EPS I, and reinforces the association of the 28-kDa EXP with virulence. However, since P. solanacearum mutants lacking only the 28-kDa EXP produced wild-type amounts of EPS I and were fully virulent, the function of this protein remains unclear.