Figure 7. hHP1β dimerization is required for maintaining condensed cellular chromatin states.

(a) Schematic diagram of the transgene system used to test chromatin compaction effects of hHP1β. A tandem array of the construct has been integrated into the genome of U2OS mammalian cells. Dox, doxycycline; rtTA, reverse tetracycline-controlled TET-VP16 transactivator, whose binding to tetracycline responsive elements (RE) is activated by doxycycline. (b) Together with mCherry-LacI, the indicated fusion proteins were transiently expressed in U2OS cells containing the chromatin reporter array as described in a. Representative confocal images in the absence or after induction of transcription from the array with doxycycline (Dox) are shown. DNA was stained with DAPI. Inlets show enlarged chromatin reporter array; scale bar, 10 μm. (c) Quantification of the results shown in b together with results of similar experiments using additional hHP1β mutant proteins. Averages of three independent experiments are plotted; error bars represent s.d.; n>300 for each condition; asterisks represent P<0.05 according to Student's t-test.