title: Cloning and characterization of tek, the gene encoding the major extracellular protein of Pseudomonas solanacearum.
abstract: Susceptible plants infected by Pseudomonas solanacearum usually will, 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 radiolabeled 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 extracellularly 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.
authors.affiliation: Department of Plant Pathology, University of Georgia, Athens 30602, USA. TDenny@uga.cc.uga.edu
authors.forename: T P
authors.initials: TP
authors.lastname: Denny
authors.forename: L M
authors.initials: LM
authors.lastname: Ganova-Raeva
authors.forename: J
authors.initials: J
authors.lastname: Huang
authors.forename: M A
authors.initials: MA
authors.lastname: Schell
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D003001:Cloning, Molecular; D004269:DNA, Bacterial; D005798:Genes, Bacterial; D008565:Membrane Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis; D011549:Pseudomonas / Q000235:genetics* / Q000472:pathogenicity; D014774:Virulence / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D008565:Membrane Proteins; D011135:Polysaccharides, Bacterial; C099519:Tek protein, Pseudomonas