Cyclization of Globular DNA. Implications for DNA−DNA Interactions in Vivo

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Abstract
The rate of cyclization of λ DNA varies over more than 6 orders of magnitude, from 3.2 × 10-7 s-1 to 2 s-1, in a Tris−EDTA buffer as a function of spermidine concentration. This variation is strictly correlated with the conformation of the chain. The highest rates are obtained when the chain is collapsed into a dense globular state. The effective concentration of the chain ends in the reaction is then 87 000-fold greater than in the random coil state. These results show that DNA globularity must be taken into account to understand biological processes involving intramolecular DNA−DNA interactions.