Fig. 3: PICH decreases nucleosome lifetimes and lowers the force required to achieve nucleosome unwrapping.
a Representative Distance-Time traces showing inner-turn-unwrapping events of nucleosomes at 10 pN, 12.5 pN and 15 pN, in the absence (i) and presence (ii) of PICH and ATP. Horizontal lines indicate segments detected by a step-fitting algorithm (see Methods). Unwrapping events are highlighted by the vertical dashed lines. b CPDs of nucleosome lifetimes in the absence of PICH at a constant force of 10, 12.5 or 15 pN, respectively. Solid lines display the corresponding bi-exponential decay fits. N = 50, 41 and 48 nucleosome lifetimes for 10, 12.5 and 15 pN, respectively. c CPDs of the nucleosome lifetimes shown in (b) (light blue) and CPDs of nucleosome lifetimes in the presence of PICH and ATP (purple) at 10 pN (i); 12.5 pN (ii); and 15 pN (iii). Solid lines display the corresponding bi-exponential decay fits. N = 45, 74 and 67 nucleosome lifetimes in the presence of PICH and ATP for 10, 12.5 and 15 pN, respectively. Red data points in (i) show the CPD of nucleosome lifetimes (N = 34) at 10 pN in the presence of PICH and AMP-PNP. d Bar chart showing the mean lifetimes of the major population of nucleosomes as determined by the fits shown in (b and c). Data are presented as mean lifetimes ± standard error of the fits. For N of the total populations, see (b and c). e Fits of an Arrhenius-type equation (Eq. 2) to the tetrasome-corrected unwrapped fractions of nucleosomes in the absence (light blue) and presence (purple) of PICH and ATP (solid squares). The open squares reflect the measured unwrapped fractions, as shown in Fig. 2d, with Ntotal = 421 and 425 nucleosomes in the absence and presence of PICH and ATP, respectively. Data are presented as unwrapped fractions ±95% CIs. The half forces (F1/2) for inner-turn unwrapping derived from the fits are indicated. f A plot showing the percentage increase in the probability of inner-turn nucleosome unwrapping due to the presence of PICH and ATP. Data were obtained from a subtraction analysis of the sigmoidal curves displayed in (e). Source data are provided as a Source Data File.
