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The DNA 4 coding region of banana bunchy top virus from a Chinese Zhangzhou isolate (BBTV-ZZ) is cloned by PCR. The sequencing analysis shows that it is 351 nucleotides long and it putatively encodes a protein of 116 amino acids. On the basis of a plant binary vector pBin438, the plant expression vector pBBTV-4B harboring the BBTV-ZZ DNA 4 coding region has been constructed and then transferred to tobacco (Nicotiana tobacum cv. Xanthi nc) by a Agrobacterium-mediated procedure. Under insect-free condition, movement-defective mutant of CMV-Fny strain (CMV-Fny-△MP) is mechanically inoculated on the lower leaves of transgenic plants. Systemic symptoms with different degrees of severity are developed in the upper uninoculated leaves of transgenic plants at 12 days postinoculation (dpi), while no symptoms can be seen in the uninoculated leaves of untransformed plants at any time. Accumulation of CMV-Fny is detected on the upper uninoculated leaves of transgenic plants, but is not on that of untransformed plants by indirect double antibody sandwich enzyme-link immunosorbent assay (DAS-ELISA). The results reveal that transgenic plants have acquired the property of cell-to-cell movement and systemic spread of CMV-Fny-△MP. This suggests that the protein encoded by BBTV-ZZ DNA 4 might have function of viral movement protein.