Fig. 4. ABCG2 exists as a disulfide-linked dimer. Total cell lysates from stably transfected HEK293 cells were analyzed by SDS-PAGE and western blotting. To avoid formation of non-natural disulfide bridges 10 mM N-ethylmaleimide was included in both the lysis buffer and in the SDS loading buffer. The samples were incubated in the SDS loading buffer with or without 100 mM DTT as indicated for 30 minutes before application to the gel. For the immunoblotting we used both HA antibody (upper panel, IB:HA) and MYC antibody (lower panel, IB:cmyc).