Characterization of the replication and stability regions of Agrobacterium tumefaciens plasmid pTAR

A 5.4-kilobase region containing the origin of replication and stability maintenance of the 44-kilobase Agrobacterium tumefaciens plasmid pTAR has been mapped and characterized. Within this region is a 1.3-kilobase segment that is capable of directing autonomous replication. The remaining segment contains the stability locus for maintenance of pTAR during nonselective growth. Approximately 35% of pTAR shares sequence homology with pAg119, a 44-kilobase cryptic plasmid in grapevine strain 1D1119. However, no homology was detected between pTAR DNA and several Ti plasmids or several other small cryptic plasmids in many A. tumefaciens strains. A recombinant plasmid containing the origin of replication and stability maintenance region of pTAR was compatible with pTiC58, pTi15955, and pTi119 and incompatible with pAg119. A new compatibility group, Inc Ag-1, is discussed.