text: The structure of a transcription factory appears to be determined by cell type, transcriptional activity of the cell and also the method of technique used to visualise the structure. The generalised view of a transcription factory would feature between 4 – 30 RNA polymerase molecules and it is thought that the more transcriptionally active a cell is, the more polymerases that will be present in a factory in order to meet the demands of transcription. The core of the factory is porous and protein rich, with the hyperphosphorylated, elongating form polymerases on the perimeter. The type of proteins present include: ribonucleoproteins, co-activators, transcription factors, RNA helicase and splicing and processing enzymes. A factory only contains one type of RNA polymerase and the diameter of the factory varies depending on the RNA polymerase featured; RNA polymerase I factories are roughly 500 nm in width whereas RNA polymerase II and III factories a magnitude smaller at 50 nm. It has been experimentally shown that the transcription factory is immobilised to a structure and it is postulated that this immobilisation is because of a tethering to the nuclear matrix; this is because it has been shown it is tied to a structure that is unaffected by restriction enzymes. Proteins that have been thought to be involved in the tethering includes spectrin, actin and lamins.