Hela cells were transfected with vectors encoding epitope-tagged erlins, or empty vector, and cell lysates were prepared. In A, lysates were subjected to either native-PAGE or SDS-PAGE and were probed as indicated, with the migration positions of molecular mass markers indicated (masses in kDa). In B, lysates were incubated with anti-E2 or rabbit polyclonal anti-HA [10] and immunoprecipitates were subjected to SDS-PAGE and were probed as indicated. Note that mouse monoclonal anti-E1 is human specific [9,12] and recognizes endogenous E1, but not exogenous E1HA. E1, E2, E1HA and E2HA migrated, respectively, at 41,43, 42 and 44 kDa.