IDENTIFICATION OF A LOCUS THAT REGULATES MULTIPLE FUNCTIONS IN PSEUDOMONAS-SOLANACEARUM

When Pseudomonas solanacearum K60 carries a multicopy plasmid containing cosmid clone pE6C (from the wild-type strain K60) or pBE6 (from the nonpathogenic strain B1), several phenotypic changes are observed, including the following: loss of virulence, reduced extracellular polysaccharide production, and increased polygalacturonase activity. Both cosmids contain a common 8-kilobase DNA region that is required for the phenotype shift. Saturation mutagenesis of pBE6 with Tn3-gus suggested that a single transcriptional unit of at least 1 kilobase is responsible for the phenotype shift. In maxicell assays, subclones containing this transcriptional unit expressed a single protein of about 25 kilodaltons.