Fig. 8

Elevating Cbx7 levels increases its stability on chromatin. a Cumulative distribution of displacements for HaloTag-Cbx7 in SF8628 cells administrated with 0.1 µg per ml doxycycline replicated from Fig. 4, 1.0 µg per ml (N = 47 cells, n = 7102 displacements), and 2.0 µg per ml (N = 38 cells, n = 3543 displacements) doxycycline. The cumulative distributions were fitted with three populations. Fitted parameters are shown in Supplementary Table 9. b Normalized chromatin-bound population\(({{F}}_1^{{N}})\). Unless otherwise indicated, the superscript N represents that a given value was normalized by the Cbx7 level obtained from the immunostaining of Cbx7 (Fig. 7b) and by the chromatin-bound level at 0.1 µg per ml doxycycline. Results are means ± SD. c Survival probability distribution of the dwell times for HaloTag-Cbx7 in SF8628 cells administrated with 0.1 µg per ml doxycycline replicated from Fig. 5, 1.0 µg per ml (N = 49 cells, n = 725 trajectories), and 2.0 µg per ml (N = 64 cells, n = 907 trajectories) doxycycline. The distributions were fitted with a two-component exponential decay model. Fitted parameters are shown in Supplementary Table 10. d–f Normalized long-lived fraction (\({{F}}_{1{\mathrm{sb}}}^{{N}}\)) (d), residence time (e), and search time (f) of the long-lived HaloTag-Cbx7 population. Results are means ± SD from three biological replicates. g A proposed mechanism that underpins how increasing Cbx7 levels influences the binding and target search mechanism. Our data indicate that increasing Cbx7 levels has no effect on the number of Cbx7 molecules on the specific sites, however, increases its level bound to the non-specific sites. The residence time of Cbx7 molecules on the specific sites increases upon increasing Cbx7 levels. Increasing Cbx7 levels increases its search time, which is primarily due to the fact that Cbx7 takes more trials of the non-specific chromatin collisions to reach a specific site. The thicker arrowhead represents a longer search time and the bigger font depicts a prolonged residence time