SDS-PAGE analysis was performed using 10-12% acrylamide gels with a Bis-Tris buffer system (Invitrogen). Western blots were performed with Alexa Fluor 688-conjugated secondary antibodies (Molecular Probes), and were quantitated using an Odyssey Infrared Imaging system and Odyssey InCell Western software (LI-COR Biosciences) [30] . Standard curves with purified E proteins confirmed the linearity of this analysis (data not shown).