Cells and Viruses-HeLa cells were grown in Dulbecco's modified Eagle's medium ϩ Glutamax (Invitrogen) supplemented with 10% fetal calf serum, 100 g/ml streptomycin, and 100 IU/ml penicillin. Human adenovirus type 5 (Ad5) was propagated as described previously (33) and purified using a ViraBind adenovirus purification kit (Cellbiolabs). The HeLa cell line stably expressing GFP-tagged ribosomal protein RPL27 has been reported elsewhere (34) . For microscopy, HeLa cells were grown on glass coverslips in 6-well dishes.