Interaction of EBNA-LPR1 with EBNA-LPR4 in mammalian cells. COS-7 cells transiently expressing the indicated proteins were immunoprecipitated with the mouse monoclonal antibody to the Flag epitope. The immunoprecipitates were subjected to electrophoresis on a denaturing gel, transferred to a nitrocellulose sheet, reacted with the mouse monoclonal antibody to EBNA-LP (A), and then reprobed with anti-Flag antibody (B). One-tenth of the COS-7 whole-cell extract (WCE) input in immunoprecipitation reactions for lanes 1, 2, and 3 was loaded in lanes 4, 5, and 6, respectively. Positions of molecular mass markers are on the left. W.B., Western blot.