Determination of Oligomeric State and Role of the Acidic C Terminal Tail of Vaccinia Virus I3 Single Stranded DNA Binding Protein

Single-stranded DNA (ssDNA) binding proteins (SSB) play a major role in DNA replication, recombination, and repair, by protecting ssDNA from nuclease attack and removing inhibitory secondary structure. Poxviruses are large double stranded DNA viruses that replicate within the cytoplasm of cells, and must encode their own DNA replication proteins. Previous work has identified the Vaccinia I3 protein as the virally encoded SSB. The structure of I3 has not been solved and the amino acid sequence lacks conservation to other SSB proteins, excepting an acidic C terminus. Our work has shown that I3 can form dimeric and tetrameric complexes. Removal of the C terminus prevents tetramer formation and increases the affinity for ssDNA. We have demonstrated that the C terminus is surface exposed and can compete with ssDNA for SSB binding. The C terminus plays a role in virus infection, as its obstruction decreases the amount of viral DNA replication.