Involvement of circular intermediates in the transfer of T-DNA from Agrobacterium tumefaciens to plant cells

Co-cultivation of Agrobacterium tumefaciens with plant cells leads to the induction of circular copies of the T-DNA segment of the large tumour-inducing (Ti) plasmid in the bacterial cells. These circular molecules are presumably intermediates in DNA transfer from the A. tumefaciens genome to the plant cells. In support of this suggestion, the junction of the T-DNA circles occurs precisely in the 25-base pair terminal sequence involved in T-DNA transfer