Volume 3

Gene expression / Benjamin Lewin.

  • Lewin, Benjamin.
Date:
1974-1977
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Gene expression / Benjamin Lewin. Source: Wellcome Collection.

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    bottom fractions on gradient bottom fractions on gradient < 2 O O o O CD X cu Figure 3.20: site of the nick introduced by relaxation of Col El DNA. The upper panel shows the two strands, circular (C) and linear (L), separated on alkaline sucrose gradients after open circles have been denatured. The lower panel shows the three fragments obtained after the relaxed Col El DNA has been treated with Eco RI nuclease; A represents a linear strand of 2.1 X 10 6 daltons (the product of a single break in the circular strand C of the upper panel); B and C represent the products of the linear strand L of the upper panel, and are fragments of 1.7 X 10 6 and 0.4 x 10® daltons. Data of Lovett, Guiney and Helinski (1974). recentrifuged through CsCl in the presence of poly(U.G), it proves to comprise the H strand. This is the strand that is nicked. Lovett and Helinski (1975) demonstrated that the protein remaining associated with the nicked strand of Col El DNA is a single species of molecular weight 60,000 daltons; the other proteins of the relaxation complex, which in clude two major components of 17,000 and 11,000 daltons as well as several minor components, are lost at this stage of isolation of the dena tured DNA. Since the buoyant density shift of the denatured strand corresponds to association with about 60,000 daltons of protein, this suggests that a single molecule of the protein is associated with each nicked strand of DNA.