Transcription factories are nuclear subcompartments that remain in the absence of transcription

Nascent transcription occurs at nuclear foci of concentrated, hyperphosphorylated RNA polymerase II (RNAPII). We investigate RNAPII localization, distal gene coassociation, and Hbb locus conformation during inhibition of transcription. Our results show distal active genes remain associated with RNAPII foci and each other in the absence of elongation. When initiation is inhibited, active genes dissociate from RNAPII foci and each other, suggesting initiation is necessary to tether distal active genes to shared foci. In the absence of transcription RNAPII foci remain, indicating they are not simple accumulations of RNAPII on transcribed genes but exist as independent nuclear subcompartments.