A conserved zinc finger motif in the coat protein of Tomato leaf curl Bangalore virus is responsible for binding to ssDNA

Summary. Tomato leaf curl Bangalore virus (ToLCBV-[Ban5]) from south India belongs to the genus Begomovirus of the family Geminiviridae. So far, only the DNA A component has been identified in this virus. In this paper we report the overexpression of ToLCBV-[Ban5] coat protein (CP) in E. coli and its characterization. The purified recombinant CP bound preferentially to ssDNA in a sequence non-specific manner. Deletion of 50 amino acids from the N-terminus, including a putative N-terminal helix, did not result in the loss of binding to DNA. A search for motifs responsible for DNA binding indicated a conserved putative zinc finger motif in the CPs (corresponding to residues 65–85 in ToLCBV-[Ban 5] CP) of begomoviruses. The role of this motif in DNA binding was evaluated through site-directed mutagenesis of the conserved cysteines (C68, C72) and histidines (H81, H85) present within this motif to alanine. The results indicate that the zinc finger motif is indeed involved in binding to zinc and DNA.