In bacteria, chromosomes are circular and DNA seems to be organized into independent topological domains (Delius and Worcel, 1974; Sinden and Pettijohn, 1981; Postow et al, 2004), in which different levels of helical tension can be modulated.
Therefore, the issue of whether DNA is organized into closed topological domains in which helical tension is constrained is less clear and remains controversial (Eissenberg et al, 1985; Esposito and Sinden, 1988; Freeman and Garrard, 1992).
Analogously, DNA helical tension also builds up in front of DNA replication forks (Schvartzman and Stasiak, 2004).
In the yeast Saccharomyces cerevisiae, as both topoisomerase I and II can relax and helical tension, the presence of either one of the two enzymes suffices for transcription to proceed (Kim and Wang, 1989).
Consequently, positive DNA helical tension increases in front of an advancing polymerase and negative DNA helical tension arises behind it (Liu and Wang, 1987).
Helical tension and compression springs have numerous uses, notably automobile suspension systems, gun-recoil mechanisms, and closing valves on engines.
As the potential to generate DNA helical tension depends on the amount of transcribed DNA (bp) per time unit, we estimated this parameter as the transcript length times gene transcription rate (García-Martínez et al, 2004).
DNA helical tension also promotes the formation of supercoils that contribute to the juxtaposition of distant DNA sites and to the global folding of DNA (Huang et al, 2001).
Consequently, helical tension builds up to lower values towards the telomere.
How DNA helical tension is constrained along the linear chromosomes of eukaryotic cells is poorly understood.
The helical tension of DNA has deep implications in most genome transactions.
