Local denaturation of DNA by shearing forces and by heat

Hershey, A. D., Goldberg, E., Burgi, E., Ingraham, L. (March 1963) Local denaturation of DNA by shearing forces and by heat. J Mol Biol, 6. pp. 230-43. ISSN 0022-2836 (Print)0022-2836 (Linking)

URL: https://www.ncbi.nlm.nih.gov/pubmed/13954121
DOI: 10.1016/S0022-2836(63)80072-8


The DNA of phage T5 is partially denatured by stirring at 25°C in 0·1 M- or 0·6 M-NaCl at speeds and DNA concentrations similar to those required to initiate breakage of the molecules. The denaturation can be recognized by abnormal retention of the DNA on fractionating columns and by limited susceptibility to enzymes specific for denatured DNA, but not by alteration of absorbancy—temperature relationships. These measurements show that a small degree of denaturation affects a large fraction of the molecules, which must be denatured in restricted regions along their length. The lesions cannot be healed by thermal treatment. After partial breakage of a DNA sample by stirring, broken and unbroken molecules prove to be denatured about equally. Denaturation but not breakage is suppressed when DNA is stirred at 5°C or in 2·6 M-NaCl. Conversely, denaturation without breakage can be produced at 45°C and diminished stirring speeds. Fast stirring, sufficient to break the DNA quickly, reduces the amount of denaturation. Thus breakage and denaturation are independent processes in that they do not show any marked tendency to occur simultaneously in a single molecule, nor does one predispose to the other. Stirring first at 5°C at the speed producing half-length fragments, then restirring at a higher temperature, causes less denaturation than stirring at the higher temperature only. This means that denaturation, like breakage, is produced by forces acting near the centers of the molecules, forces whose effectiveness depends both on the conditions of stirring and on the length of the molecules. Local denaturation can be produced also by bringing T5 DNA to temperatures near the midpoint of the hyperchromic transition and then cooling either rapidly or slowly. Probably heat and shear act in part through similar mechanisms. The DNA of phage T2 is also subject to denaturation under shear, but is appreciably less susceptible than T5 DNA.

Item Type: Paper
Uncontrolled Keywords: *Coliphages *Dna *DNA, Viral *Hot Temperature *Heat
Subjects: bioinformatics > genomics and proteomics > genetics & nucleic acid processing > DNA, RNA structure, function, modification
Investigative techniques and equipment
CSHL Authors:
Communities: The Carnegie Institution Department of Genetics
Depositing User: Matt Covey
Date: March 1963
Date Deposited: 19 Apr 2017 20:24
Last Modified: 19 Apr 2017 20:24
Related URLs:
URI: https://repository.cshl.edu/id/eprint/34500

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