Figure 4.

Transient expression of the dominant negative Nopp140 carboxyl terminus chases snoRNPs out of the nucleolus (A) and arrests RNA pol I transcription (B) without affecting the localization of RNA pol I (C). Cells were transfected with the HA-tagged carboxyl terminus of Nopp140, and subsequently endogenous GAR1 (a) and RNA pol I (c) were labeled by indirect double immunofluorescence or run-on transcription was detected by BrUTP incorporation and visualization with anti-BrdU antibodies (b). The transfected cells (solid arrows) were identified with anti-HA antibodies (a′ and c′) or by the aberrant nucleoplasmic distribution of endogenous Nopp140 detected with Nopp140-specifc antibodies (b′). All nucleoli can be clearly identified in the phase-contrast images (a′′, b′′, and c′′). One nucleolus of a transfected and an untransfected cell is marked in each panel (small open arrows). Bar, 10 μm.