Novel genes involved in the regulation of pathogenicity factor production within the rpf gene cluster of Xanthomonas campestris

The synthesis of extracellular enzymes and extracellular polysaccharide (EP S) in Xanthomonas campestris pathovar campestris (Xcc) is subject to co-ord inate regulation by a cluster of genes called rpf (for regulation of pathog enicity factors). These genes are located within a 21.9 kb region of the ch romosome isolated as the cosmid clone pIJ3020, The genes in the left-hand s ection of this region of the chromosome have previously been characterized. This paper reports on the genes in the right-hand section and on the pheno types of mutants with transposon insertions in these genes. Sequence analys is identified eight genes or ORFs with the gene order rpfD-orf1-orf2-orf3-o rf4-recJ-rpfE-greA. Red and GreA have established functions in recombinatio n and transcriptional elongation, respectively. rpfD encoded a protein with some amino acid sequence relatedness to a hypothetical protein from Caulob acter crescentus and an autolysin response regulator in Bacillus subtilis, The predicted protein products of orf1, 2 and 3 were related to each other and had substantial amino acid sequence relatedness to hypothetical protein s from C. crescentus. Transposon insertions in orf1, 2 and 3 had no effect on the synthesis of extracellular enzymes or EPS, The predicted proteins Rp fE and Orf4 showed the highest amino acid sequence relatedness to hypotheti cal proteins from Bordetella pertussis and Klebsiella pneumoniae, respectiv ely. Transposon insertions in rpfE led to reduced levels of some extracellu lar enzymes (endoglucanase and protease) and increased levels of others (po lygalacturonate lyase). Transposon insertions in orf4 had no effect on poly galacturonate lyase but led to reduced levels of protease and endoglucanase . Levels of EPS were reduced in both rpfE and orf4 mutants, These alteratio ns in the levels of extracellular enzymes, which were relatively modest (be tween two- and threefold), did not affect the pathogenicity of Xcc on turni p. It is proposed that the gene designation should be rpf1 for orf4.