DNA from Ti plasmid present in nucleus and absent from plastids of crown gall plant cells

The Gram-negative soil bacterium Agrobacterium tumefaciens induces crown gall tumours on most dicotyledonous plants1,2, its Ti plasmids causing the neoplastic transformation of plant cells3–5. Molecular hybridization has shown that transformed cells contain a segment of the Ti plasmid (T-DN A) of molecular weight 8–15 × 106(refs 6–9), of which at least part is transcribed10,11. Some copies of the T-DNA are integrated into the plant DNA (unpublished work). In view of the prokaryotic origin of the T-DNA, the possibility of its localization within either mitochondria or chloroplasts must be considered. We present here evidence for the absence of T-DNA from mitochondria and chloroplasts. Our results clearly show its presence within the nucleus.