Fig. 7.
HP1α binding results in dynamically compacted chromatin. a FRET traces for DA1, containing no modification or H3K9me3 in the presence of 1 μM HP1α and the absence of Mg2+. b FRET trace for DA2, containing no modification or H3K9me3 in the presence of 1 μM HP1α. c FRET populations for DA1, showing H3K9me3-dependent compaction by HP1α and phosphorylated HP1α (pHP1α). d FRET populations for DA2, demonstrating close contacts induced by HP1α/pHP1α. c, d Error bars: s.e.m. For the number of traces, parameters of the Gaussian fits, see Supplementary Table 5. e Donor–acceptor channel cross-correlation analysis of DA1 in the presence of 1 μM HP1α. Fits, H3K9me0: tR,1 = 200 ± 25 ms (n = 530), H3K9me3: tR,1 = 64 ± 13 ms (72%), tR,2 = 640 ± 126 ms (28%) (n = 430). f Donor–acceptor channel cross-correlation analysis of DA2 in the presence of 1 μM HP1α. Fits, H3K9me0: tR = 123 ± 38 ms (n = 99); H3K9me3: tR,1 = 66 ± 16 ms (88%), tR,2 = 930 ± 543 ms (12%) (n = 106). Fit uncertainties correspond to 95% confidence intervals of a global fit of the indicated number of traces. For the percentage of dynamic traces, see Supplementary Table 6. e, f Error bars: s.e.m. For the number of traces, see Supplementary Table 5. g Stochastic compaction of chromatin induced by injection of HP1α at 5 s. h 2D histogram of multiple injections. Only traces exhibiting a FRET change were included in the analysis (42%). The fit yields a time constant of 1.1 ± 0.4 s (fit uncertainties correspond to 95% confidence intervals, global fit of n = 86 traces). i Model of transient stabilization of tetranucleosomes, which still retain some internal flexibility, by HP1α