1 Department of Applied Mathematics and Computer Science, Technical University of Denmark2 Department of Micro- and Nanotechnology, Technical University of Denmark3 Theoretical Biophysics, Department of Micro- and Nanotechnology, Technical University of Denmark
Two separate regimes exist for the aspect ratio of DNA. A low aspect regime where DNA will twist further under strain and a high aspect regime where DNA will untwist under strain. The question of the overall geometry, i.e. the aspect ratio, of DNA is revisited from the perspective of a geometrical analysis of transcription. It is shown that under certain reasonable assumptions transcription is only possible if the aspect ratio is in the regime corresponding to further twisting. We find this constraint to be in agreement with long-established crystallographic studies of DNA.