SEQUENCES RELATED TO TRANSPOSABLE ELEMENTS AND BACTERIOPHAGES FLANK AVIRULENCE GENES OF PSEUDOMONAS-SYRINGAE

Examination of the reported nucleotide sequences containing avirulence genes of Pseudomonas syringae pathovars suggested that avrA, avrB, av rC, avrPphC, avrRpm1, and avrPpiA1 are bordered by sequences similar t o those of transposable elements of gram-negative bacteria. Repeat seq uences and fragments of at least two different insertion sequence elem ents were identified at the ends of avrA and avrB, implying multiple t ransposition events for these areas, A DNA region homologous to a bact eriophage sequence was found upstream of avrPto, The linkage of variou s virulence/avirulence genes of animal- and plant-pathogenic bacteria with transposable elements and bacteriophage sequences, together with the presence of several of these genes on plasmids, supports the idea of horizontal transfer and frequent exchange of virulence/avirulence g enes among bacterial pathogens.