Many proteins in the current nucleolar proteome were not readily visualized in the nucleolus by fluorescence microscopy. However, our data show that even in these cases quantitative changes in nucleolar content are reflected in visible changes in protein distribution. For example, U2AF 65 , hnRNPU, and SFPQ (also known as PSF) are all known to be involved in mRNA metabolism, and at least U2AF 65 has been shown to play a role in adenovirus mRNA metabolism (38, 52, FIG. 5 . Distribution of proteins identified by 2D as being depleted from nucleolus during viral infection. All the images are of a fixed focal plane ϳ0.3 m in depth, the DAPI stain is in blue in all cases, and the bar represents 10 m. A and B, in each case the top row of images is representative of the location of the indicated endogenous protein or expressed tagged fusion protein in Ͼ80% of cells examined. The second row of images shows the same indicated endogenous or expressed tagged protein in cells infected with adenovirus for 18 h. Viral infection was confirmed by anti-DBP serum. In addition, as indicated in the images, a control nucleolar antigen (UBF or B23) is also shown in the uninfected cells.