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What is the minimum length of a DNA molecule for the ends to come in close enough contact that they can ligate. Assume there are free divalent cations in solution. Does anyone have any idea?

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I stumbled across this paper demonstrating it is between 150-200 base pairs.

DNA flexibility studied by covalent closure of short fragments into circles D Shore, J Langowski, and R L Baldwin PNAS 1981 78 (8) 4833-4837

http://www.pnas.org/content/78/8/4833.full.pdf

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good source - ligation still occurs at 126 bp but much less efficiently... at some point there, the DNA is too stiff to flop around and join in the ligase catalytic site. –  shigeta Mar 12 at 5:36
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Yes, and in the last sentence the authors suggest that the exact number of base pairs will become important at these lengths: "If the number of bp in the DNA fragment is not an integral multiple of the helix repeat,then the need to twist the DNA helix in order to make strand ends meet may [make ligation difficult] for sizes less than 500bp." –  Alan Boyd Mar 12 at 5:55

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