Fig. 2. Activation of RNA polymerase II by removal of DRB. (A) Integrated fluorescent intensity of HCMV IE transcripts accumulated in the nuclear foci relative to the integration site. Removal of DRB resulted in a rapid accumulation of HCMV IE mRNAs at nuclear foci. (B) Integrated fluorescent intensity of HCMV IE transcripts dispersed through the nucleoplasm relative to negative nuclei. The amount of HCMV IE mRNAs in the remainder of the nucleoplasm increased at a slower rate after DRB removal. Transcripts radiating from the nuclear foci were observed from approximately 5 minutes onwards. (C) CSLM images of cells at different times after RNA polymerase II inactivation. After induction of the HCMV IE gene expression by cycloheximide, transcripts were present in nuclear foci and also dispersed throughout the nucleoplasm. Two hours of DRB inhibition removed virtually all transcripts from the nucleus. Subsequent removal of DRB resulted in a fast increase of fluorescent intensity at nuclear foci (
3 minutes and later), followed by the nucleoplasm. Untreated cells were not subjected to cycloheximide or DRB treatment; therefore these cells did not express the HCMV IE genes.
