In the presence of spermidine, the DNA molecule of the bacteriophage l
ambda undergoes a coil-globule transition. We report here that the cyc
lization of this molecule in its globular state is greatly accelerated
(by more than 10(4)-fold) in comparison with the cyclization reaction
taking place in the coil conformation. ((C) Academie des sciences/Els
evier, Paris.).