Epstein–Barr nuclear antigen 1 is a multifunctional, dimeric viral protein associated with Epstein–Barr virus . It is the only EBV protein found in all EBV-related malignancies. It is important in establishing and maintaining the altered state that cells take when infected with EBV. EBNA1 has a glycine–alanine repeat sequence that separates the protein into amino- and carboxy-terminal domains. This sequence also seems to stabilize the protein, preventing proteasomal breakdown, as well as impairing antigen processing and MHC class I-restricted antigen presentation. This thereby inhibits the CD8-restricted cytotoxic T cell response against virus-infected cells. EBNA1 is expressed from the Qp promoter during all latency programs. It is the only viral protein expressed in latency program I.