Summary: The replication genes () of the virulence plasmid pYVe439-80 of were localized and characterized by restriction endonuclease analysis. Comparison with pIBl, a virulence plasmid of , indicates that while the plasmids carry homologous genes their location with respect to the highly conserved “calcium region” is different. This replication function is thermosensitive. Mini-derivatives of pYVe439-80 appear to be rather unstable. The region of pYVe439-80 containing homology to the determinant of F was shown to contain a plasmid-stabilization system (). The region encoding was characterized by restriction endonuclease analysis. pIBl contained an homologous region but located differently. The pYV plasmids thus underwent rearrangements during their divergent evolution. While the positions of and in the two plasmids are inverted with respect to the surrounding loci, our determination of the orientation of each locus rules out the hypothesis of a simple inversion of a quadrant of pYV. The gene encoding YOP5, a 26 kDa protein encoded by pIBl, was cloned on a mobilizable vector and introduced in W22708 containing pYVe227 (indistinguishable from pYVe439-80), mutated in the homologous gene. The recombinant secreted YOP5. Hence, the transcriptional activation and secretion systems of pYVe227 act on a gene from pIBl and on its product, indicating that these systems are interchangeable.


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