Identification of C-terminal amino acid residues of cauliflower mosaic virus open reading frame III protein responsible for its DNA binding activity.

We cloned in Escherichia coli truncated versions of the protein p15 encoded by open reading frame III of cauliflower mosaic virus. We then compared the ability of the wild-type p15 (129 amino acids) and the deleted p15 to bind viral double-stranded DNA genome. Deletions of > 11 amino acids in the C-terminal proline-rich region resulted in loss of DNA binding activity of wild-type p15. Moreover, a point mutation of the proline at position 118 sharply reduced the interaction between the viral protein and DNA. These results suggest that cauliflower mosaic virus p15 belongs to the family of DNA binding proteins having a proline-rich motif involved in interaction with double-stranded DNA.