Identification of the nicking tyrosine of geminivirus Rep protein.

The replication initiator (Rep) proteins of geminiviruses perform a DNA cleavage and strand transfer reaction at the viral origin of replication. As a reaction intermediate, Rep proteins become covalently linked to the 5' end of the cleaved DNA. We have used tomato yellow leaf curl virus Rep protein for in vivo and in vitro analyses. Isolating a covalent peptide-nucleotide complex, we have identified the amino acid of Rep which mediates cleavage and links the protein to DNA. We show that tyrosine-103, located in a conserved sequence motif, initiates DNA cleavage and is the physical link between geminivirus Rep protein and its origin DNA.