A region of a Sym plasmid of Rhizobium leguminosarum biovar phaseoli has similarity to prokaryotic insertion sequences and to eukaryotic integrases.

Near the nod and nif genes of the Sym plasmid pRP2JI of Rhizobium leguminosarum biovar phaseoli are three open reading frames whose deduced polypeptide products have similarities to those of genes in bacterial insertion sequences. The similarity of one of these ORFs was significantly greater to that of the integrase region of pol proteins of eukaryotic retroviruses and transposable elements in animals and plants than it was to the transposases of prokaryotic insertion sequences. In the noncoding region of the IS-like element, there was a sequence similar to that which had been identified close to nod genes in Azorhizobium caulinodans.