Fig. 4.

CtIP dissociates from circular complexes upon DNA unfolding. (A) Kymographs displaying the unfolding of three circularized λ-DNA–CtIP complexes with local compactions upon photoinduced breaking of the DNA. Arrows indicate where the DSB occurs, which corresponds to the position from where the DNA starts to unfold. Upon unfolding, the local compaction disappears. (B) Schematic illustration showing the unfolding event, where the proteins causing a local compaction dissociate as the DNA is unfolding. (C) Kymographs of unfolding of five λ-DNA–CtIP complexes, in which two circles are joined through a central static local compaction. The arrows indicate the initiation of DNA unfolding upon photoinduced breaking. As the broken DNA end unfolds, the local compaction disappears once the end has reached the center and the linear molecule is separated from the other circular DNA (clearly discernible in kymographs 1 and 2). The extensive illumination generates additional breaks causing fragmentation of the linearized DNA (3), as well as breaking and unfolding of the remaining circular molecule (4 and 5). (D) Schematic illustration showing the unfolding of two circularized λ-DNA–CtIP complexes joined through a local compaction. Upon breaking, the proteins causing the local compaction will dissociate, and the DNA molecules will separate. The vertical and horizontal scale bars correspond to 5 s and 3 µm, respectively.