Figure 3.

Qualitative examination of linearized pUC19 incubated with either recombinant Ku (A and B) or HeLa Ku (C and D) revealed the formation of Ku-associated loops. Clusters of Ku particles were common (arrows in B and D). For statistical analysis, a 660-bp DNA fragment was used to quantitate the looping effect initially observed for Ku and DNA-PK on linearized pUC19. For these studies, all samples were mounted and imaged without fixation. (E–H) Examples of looped 660-bp DNA formed in the presence of recombinant Ku. (I) Multi-DNA complexes were also observed at an increased frequency in the presence of recombinant Ku. (J–M) Loops formed in the presence of Ku and the DNA-PKcs. A free DNA-PKcs particle is visible in the lower right corner of J. Bar in M is 100 nm for A–C and E–M. Bar in D is 100 nm for D.