Inhibition of pol I transcription by ActD does not prevent traYc of nucleolar proteins. However, if the diVusion coeYcient of nucleolar proteins in the nucleoplasm is similar for active and repressed pol I transcription, the traYc in segregated nucleoli changes diVerently for diVerent nucleolar components. TraYc of UBF in the nucleolus is decreased by ActD, whereas it is similar for nucleolin or increased for ribosomal proteins (Chen and Huang 2001) .