Epstein-Barr virus nuclear antigen 1 forms a complex with the nuclear transporter karyopherin alpha 2

The Epstein-Barr virus (EBV) is implicated in the induction of several malignancies, The nuclear antigen 1 (EBNA1) is the only viral protein that is expressed consistently in all EBV-associated tumors. EBNA1 is involved in the replication and maintenance of the viral episome in the infected cell and exhibits oncogenic activity in transgenic mice, Here we report the identification of the nuclear transporter karyopherin alpha 2 as a cellular partner of EBNA1 using the yeast ''two-hybrid system.'' Karyopherin alpha 2 is also called importin alpha or Rch1. The binding to karyopherin alpha 2 was mediated through a C-terminal region of EBNA1 encompassing the nuclear localization signal, whereas clones of EBNA1 devoid of the nuclear localization signal failed to bind to karyopherin alpha 2. The interaction was biochemically confirmed by far-Western analysis using bacterially expressed karyopherin alpha 2 and karyopherin alpha 2-specific monoclonal antibodies. The nuclear transport of EBNA1 was impaired by expression of N-terminally truncated karyopherin alpha 2. Zone velocity sedimentation in a sucrose gradient indicated that: (i) EBNA1 and Rch1 colocalize; and (ii) the association of karyopherin alpha 2 with high molecular weight protein complexes might be impeded by the presence of EBNA1.