A gene was previously cloned from Pseudomonas syringae pv. glycinea race 6, designated avirulence gene A (avrA), that controls the expression of virulence by the pathogen on specific cultivars of soybean. A 3.2-kilobase (kb) AccI subclone from the cosmid clone pPg6L3 was shown to be active when cloned into the broad-host-range vector pRK404. Transposon Tn5 mutagenesis and deletion analysis delineated a span of approximately 2.5 kb of DNA that was necessary for gene activity. The nucleotide sequence of a 3.409-kb segment of DNA which contained the avrA gene has been determined. An open reading frame of 2.721 kb of DNA, which correlates with the region of DNA defined by transposon mutagenesis and deletion analysis, was identified. The open reading frame would encode a protein of 100.866 kilodaltons, which is in good agreement with the 100-kilodalton protein expressed by Escherichia coli maxicells.