The study investigates the dynamic colocalization of active genes to shared transcription factories in the nucleus. Using a combination of techniques including 3D fluorescence in situ hybridization (FISH), immunofluorescence, and chromosome conformation capture (3C) assays, the researchers found that distal genes frequently colocalize with active genes at high frequencies during transcription. This colocalization is transcription-dependent, with genes moving into or out of these factories to regulate transcriptional activity. The study also highlights that active genes do not recruit and assemble transcription complexes de novo but rather migrate to preassembled transcription sites. Additionally, the findings suggest that genes with transcriptional potential are preferentially located outside chromosome territories, and that the number of transcription factories is limited in tissues, leading to competition for these sites among genes. The results provide insights into the mechanisms of gene regulation and the spatial organization of gene expression in the nucleus.The study investigates the dynamic colocalization of active genes to shared transcription factories in the nucleus. Using a combination of techniques including 3D fluorescence in situ hybridization (FISH), immunofluorescence, and chromosome conformation capture (3C) assays, the researchers found that distal genes frequently colocalize with active genes at high frequencies during transcription. This colocalization is transcription-dependent, with genes moving into or out of these factories to regulate transcriptional activity. The study also highlights that active genes do not recruit and assemble transcription complexes de novo but rather migrate to preassembled transcription sites. Additionally, the findings suggest that genes with transcriptional potential are preferentially located outside chromosome territories, and that the number of transcription factories is limited in tissues, leading to competition for these sites among genes. The results provide insights into the mechanisms of gene regulation and the spatial organization of gene expression in the nucleus.