Cyclization of short DNA fragments and bending fluctuations of the double helix

Cloutier and Widom [Cloutier, T. E. & Widom, J. (2004) Mol. Cell 14, 355-362] recently reported that the cyclization efficiency of short DNA fragments, about 100 bp in length, exceeds theoretical expectations by three orders of magnitude. In an effort to resolve this discrepancy, we tried modifying the theory. We investigated how the distribution of the angles between adjacent base pairs of the double helix affects the cyclization efficiency. We found that only the incorporation of sharp kinks in the angle distribution provides the desired increase of the cyclization efficiency. We did not find a model, however, that fits all cyclization data for DNA fragments of different lengths. Therefore, we carefully reinvestigated the cyclization of 100-bp DNA fragments experimentally and found their cyclization efficiency to be in remarkable agreement with the traditional model of DNA bending. We also found an explanation for the discrepancy between our results and those of Cloutier and Widom.