Volume 1

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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    DNA c, is included in the medium so that the structure which is visualized in the electron microscope comprises a column of basic protein collapsed around nucleic acid. After aqueous spreading, duplex DNA or DNA-RNA appears as an elongated thread; single strands of nucleic acid, however, are condensed into bushes because of random base interactions. This distinguishes clearly between duplex and single strands and allows the position of the single strands to be established relative to the duplex, whose length can be accurately measured. When the preparation is instead mounted in the presence of an appropriate concentration of formamide and salt, the duplex regions remain stable but the' random interactions which generate the bushes of single stranded nucleic acid are prevented. Single stranded sequences therefore also appear as elongated threads, although thinner and more twisted than the duplex sequences. Both single stranded and duplex contour lengths can then be measured. When two closely related but not entirely homologous DNA molecules are denatured and renatured together, the heteroduplex products of cross- renaturation are double stranded in the complementary regions but fail to anneal in regions of non-homology. (The homoduplex products of self-