Ultraviolet light irradiation of PM2 superhelical DNA
Year: 1977
Type: article
Abstract: Superhelical PM2 DNA can be photochemically modified by u.v. irradiation. The variation of S 20,w with dose shows the following characteristics. There is a linear increase from 28 to 31S produced by a low dose of u.v. irradiation (4,000 ergs/mm 2 ). A plateau in S 20,w occurs between 4,000 and 10,000 ergs/mm 2 . The S 20,w then increases when irradiation is increased to 56,000 ergs/mm 2 . Thymine dimers are introduced proportional to dose throughout the range of exposure to u.v. light. Sedimentation velocity-dye titrations reveal anomolous behavior, i.e. apparent increases in superhelix density (ρ). However, the dye-buoyant density procedure showed no change in a under the same conditions. The most satisfactory model for the data is preferential photochemical modification of premelted (possibly hairpin) sites as a greater rate than the introduction of photoproducts into duplex sites. The origin of the anomoly in the sedimentation velocity dye titrations is still unclear. “I ca'n't believe that” said Alice. “Ca'n't you??” the Queen said in a pitying tone. “Try again: draw a long breath, and shut your eyes.” Alice laughed. “There's no use trying,” she said: “One ca'n't believe impossible things.” “I daresay you haven't had much practice,” said the Queen. “When I was your age, I always did it for half-an-hour a day. Why, sometimes I've believed as many as six impossible things before breakfast…” from Through the Looking-Glass by Lewis Carroll Dedicated to the. memory of Jerryy Vinograd who belived in the impossible, twisted circular DNA and made postdoctoral life like Alice in Wonderland .
Source: Nucleic Acids Research
DOI: 10.1093/nar/4.5.1243
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W1974348328