Immunocytochemical investigations of the association of proteins with DRMs. A) NIH3T3 cells producing A-MLV were treated with PBS, TX-100 or MBCD as indicated and subsequently subjected to TX-100 extraction and stained for cav-1, GM1, CD71 and A-MLV Env as indicated. B) Background of the secondary antibody used for cav-1 staining. C) Background of the secondary antibody used for A-MLV Env staining. D) NIH3T3 cells (Env negative) stained for A-MLV Env, negative control (see text for details). Photographs were taken using an oil immersion objective, original magnification 1000×.