The Epstein-Barr virus nuclear antigen (BamHI K antigen) is a single-stranded DNA binding phosphoprotein.

The Epstein-Barr virus BamHI K nuclear antigen was shown to be phosphorylated in latently infected and virus-producing B-cell lines by in vivo labeling of cell cultures with [32P]orthophosphate and immunoprecipitation with anti-BamHI K antigen monoclonal antibody. Phosphoamino acid analysis of this protein isolated from a latently infected cell line demonstrated that the modified amino acid is phosphoserine. The BamHI K nuclear antigen transiently expressed in NIH 3T3 cells is also phosphorylated, as well as three truncated and deleted forms of the protein. Interaction of the Epstein-Barr virus BamHI K nuclear antigen with denatured DNA was examined by chromatography of wild-type and mutant forms of this protein on single-stranded DNA cellulose columns. The wild-type protein bound to denatured DNA cellulose but not cellulose alone. The BamHI K antigen remained bound to single-stranded DNA in 300 mM NaCl and eluted from the DNA at higher NaCl concentration. Similar results were obtained with 32P-labeled protein and total antigen as assayed by radioimmunoelectrophoresis. A mutant protein that lacks the glycine and alanine repeated amino acid domain and surrounding amino acids of this EBV polypeptide retained the ability to bind to denatured DNA, although it eluted at slightly lower NaCl concentration. One mutant protein that lacks the carboxyl-terminal third of the protein failed to bind to single-stranded DNA.