PT  - JOURNAL ARTICLE
AU  - Smith, Steven B.
AU  - Cui, Yujia
AU  - Bustamante, Carlos
TI  - Overstretching B-DNA: The Elastic Response of Individual Double-Stranded and Single-Stranded DNA Molecules
AID  - 10.1126/science.271.5250.795
DP  - 1996 Feb 09
TA  - Science
PG  - 795--799
VI  - 271
IP  - 5250
4099  - http://science.sciencemag.org/content/271/5250/795.short
4100  - http://science.sciencemag.org/content/271/5250/795.full
SO  - Science1996 Feb 09; 271
AB  - Single molecules of double-stranded DNA (dsDNA) were stretched with force-measuring laser tweezers. Under a longitudinal stress of ∼65 piconewtons (pN), dsDNA molecules in aqueous buffer undergo a highly cooperative transition into a stable form with 5.8 angstroms rise per base pair, that is, 70% longer than B-form dsDNA. When the stress was relaxed below 65 pN, the molecules rapidly and reversibly contracted to their normal contour lengths. This transition was affected by changes in the ionic strength of the medium and the water activity or by cross-linking of the two strands of dsDNA. Individual molecules of single-stranded DNA were also stretched giving a persistence length of 7.5 angstroms and a stretch modulus of 800 pN. The overstretched form may play a significant role in the energetics of DNA recombination.