Читать книгу Snyder and Champness Molecular Genetics of Bacteria - Tina M. Henkin - Страница 110

Some of the stress due to supercoiling of the DNA, which causes it to twist up on itself, can be relieved if the DNA is wrapped around something else, such as proteins. Sailors know about this effect: if you twist a rope in the right direction as you roll it up to store it, it does not try to unroll itself again when you are finished. Wrapping DNA around proteins in the cell is called constraining the supercoils. Unconstrained supercoils cause stress in the DNA, which can be relieved by twisting the DNA up on itself, as shown in Figure 1.26, and making the DNA more compact. The stress due to unconstrained supercoils can have other effects, as well, for example, helping to separate the strands of DNA during reactions such as replication, recombination, and initiation of RNA synthesis at promoters.