SEQUENCE-ANALYSIS OF AN INSERTION ELEMENT, IS1131, ISOLATED FROM THE NOPALINE-TYPE TI PLASMID OF AGROBACTERIUM-TUMEFACIENS

Transferred DNA (T-DNA) from several nopaline-type Ti plasmids of Agrobacterium tumefaciens was previously shown to be variable in size due to the insertion of extra DNA segments. We found an insertion sequence (named IS1131) in the T-DNA of the strain PO22 and determined the nucleotide (nt) sequence. IS1131 is 2773 bp long, contains four open reading frames, and is flanked by 12-bp perfect inverted repeats (IR). An 8-bp direct repeat was found immediately outside the IR, and represents a target site of integration. Although the IS1131 nt sequence showed a limited degree of similarity to those of the previously reported IS elements of A. tumefaciens and to the central region of T-DNA, the terminal IR of IS1131 were highly homologous (up to 83%) to those of IS66 and IS866, suggesting that these three IS elements are related to each other. A number of IS1131-related copies were found in several pathogenic, as well as nonpathogenic, nopaline-type strains from different plant sources, and were distributed on both chromosomes and plasmids.