There is much debate to whether transcription factories assemble because of the transcriptional demands of the genome or if they are stable structures that are conserved over time. Experimentally, it appears that they remain fixed over a short period of time; newly made mRNA were pulse labelled over 15 minutes and it showed no new transcription factories appearing. This is also supported by inhibition experiments. In these studies heat shock was used to turn off transcription which resulted in no change in the number of polymerases detected. Upon further analysis of western blot data it was suggested that there was in fact a slight decrease over time of transcription factories. Therefore, it could be claimed that polymerase molecules are released gently over time from the factory when there is a lack of transcription which would eventually lead to the complete loss of the transcription factory.
There is also several pieces of evidence that promotes the idea of transcription factories assembling de novo due to transcriptional demands. GFP polymerase fluorescence experiments have shown that the inducement of transcription in Drosophila polytene nuclei leads to the formation of a factory which contradicts the notion of a stable and secure structure.