Figure 5.

Effect of ATP addition on a chromatin fiber initially assembled with no ATP. Time series of extension measurements by using the transverse MT are shown, for a 49-kb DNA template. Before 180 s: After assembly of chromatin fiber at 1 pN by using untreated extracts, force was increased to 3.5 pN, the stall force for the −ATP reaction. As expected, the behavior of the fiber was similar to that observed under ATP-depleted conditions, with small step-like fluctuations plus thermal extension fluctuations. No net assembly or disassembly occurs. The behavior of the fiber is essentially the same as that observed for the ATP-depleted extract product (Figure 4C). After 300 s: After addition of +ATP extract solution into the experimental chamber, force still held at 3.5 pN. There are two main effects: the fiber tends to disassemble, and large-amplitude, apparently processive runs of extension are observed, in both assembly and disassembly directions.