DNA overstretching in the presence of glyoxal: Structural evidence of force-induced DNA melting

Leila Shokri, Micah J. McCauley, Ioulia Rouzina, Mark C. Williams

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70 Scopus citations


When a long DNA molecule is stretched beyond its B-form contour length, a transition occurs in which its length increases by a factor of 1.7, with very little force increase. A quantitative model was proposed to describe this transition as force-induced melting, where double-stranded DNA is converted into single-stranded DNA. The force-induced melting model accurately describes the thermodynamics of DNA overstretching as a function of solution conditions and in the presence of DNA binding ligands. An alternative explanation suggests a transformation into S-DNA, a double-stranded form which preserves the interstrand base pairing. To determine the extent to which DNA base pairs are exposed to solution during the transition, we held DNA overstretched to different lengths within the transition in the presence of glyoxal. If overstretching involved strand separation, then force-melted basepairs would be glyoxal-modified, thus essentially permanently single-stranded. Subsequent stretches confirm that a significant fraction of the DNA melted by force is permanently melted. This result demonstrates that DNA overstretching is accompanied by a disruption of the DNA helical structure, including a loss of hydrogen bonding.

Original languageEnglish (US)
Pages (from-to)1248-1255
Number of pages8
JournalBiophysical journal
Issue number3
StatePublished - Aug 1 2008

Bibliographical note

Funding Information:
This work was supported in part by National Institutes of Health grant GM 072462 and National Science Foundation grant MCB-0744456.


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