Phosphorylation of the Adenovirus DNA-Binding Protein and Epitope Mapping of Monoclonal Antibodies against It

To facilitate structure/function studies of the adenovirus type 2 or 5 single-stranded DNA binding protein (DBP), the epitopes of five anti-DBP monoclonal antibodies were mapped. Antibodies 37-3, 38-2, and B6 mapped between DBP residues 131-174 which corresponds to the host-range or hinge region of the molecule. The epitopes for antibodies 16-5 and 18-9 mapped between residues 56-81, and included a phosphorylated serine at position 70. Using antibodies 16-5 or 18-9 as analytical reagents, ∼1/2 of the DBP molecules present at late times in infected HeLa cells were found to be phosphorylated at serine 70. A similar pattern of serine 70 phosphorylation was observed in productively and abortively infected monkey cells as well as in an E2A-transformed, DBP expressing cell line. This study also reports the preliminary identification of two new phosphorylation sites on Ad2 DBP at serines 160 and 161 (corresponding to serine 161 on Ad5 DBP). No differences were observed in the phosphorylation of serine 160/161 in DBP isolated from infected HeLa cells or from productively and abortively infected monkey cells. Therefore, phosphorylation of these sites cannot account for the block to wild-type adenovirus growth in monkey cells.