Linus Pauling showed evidence for a helix and planar base stacking along the helix axis. Early in 1953 Watson and Crick proposed a correct structure for the DNA double helix. Pauling later cited several reasons to explain how he had been misled about the structure of DNA, among them misleading density data and the lack of high quality X-ray diffraction photographs. During the time Pauling was researching the problem, Rosalind Franklin in England was creating the world's best images. They were key to Watson's and Crick's success. Pauling did not see them before devising his mistaken DNA structure, although his assistant Robert
DNA supercoil and once again it is (in part at least) relieved by superhelicity, but this time in the opposite direction ("i.e.," left-handed or "positive"). Each left-handed tertiary supertwist removes a single, now "undesirable" right-handed Watson-Crick secondary twist. The titration ends at pH 13, where Form IV appears. DNA supercoil DNA supercoiling refers to the over- or under-winding of a DNA strand, and is an expression of the strain on that strand. Supercoiling is important in a number of biological processes, such as compacting DNA, and by regulating access to the genetic code, DNA supercoiling strongly affects DNA metabolism and possibly gene