Fig. 3

Transcription DNA, supercoiling and chromosome architecture. Data from chromosome conformation capture experiments indicate that long, heavily-transcribed transcription units can form barriers to DNA-DNA interaction [16]. The transcribed region (red) has few plectonemes and insulates the flanking regions that are rich in plectonemically interwound DNA. Cessation of transcription in the red zone allows plectonemic wrapping of DNA to be restored, re-establishing DNA-DNA contacts and allowing interactions between the red zone and the flanking regions. Activating and inhibiting transcription in the red region lowers and raises, respectively, the barrier that insulates it from its neighbouring genomic regions. The insulating mechanism does not involve influencing supercoil diffusion, nor is it dependent on translation of the transcripts within the heavily transcribed region