SILAC Labeling of HeLa Cells and Nucleolar Isolation-Isolation of purified nucleoli from uninfected and infected cells was performed as described previously (29) . For both SILAC and standard 2D gel analysis, 10 8 HeLa cells were infected at a multiplicity of infection (m.o.i.) of 5 with Ad5 and harvested at 18 h postinfection.