RuvB-like ATPases Function in Chromatin Decondensation at the End of Mitosis

Chromatin undergoes extensive structural changes during the cell cycle. Upon mitotic entry, metazoan chromatin undergoes tremendous condensation, creating mitotic chromosomes with 50-fold greater compaction relative to interphase chromosomes. At the end of mitosis, chromosomes reestablish functional interphase chromatin competent for replication and transcription through a decondensation process that is cytologically well described. However, the underlying molecular events and factors remain unidentified. We describe a cell-free system that recapitulates chromatin decondensation based on purified mitotic chromatin and Xenopus egg extracts. Using biochemical fractionation, we identify RuvB-like ATPases as chromatin decondensation factors and demonstrate that their ATPase activity is essential for decondensation. Our results show that decompaction of metaphase chromosomes is not merely an inactivation of known chromatin condensation factors but rather an active process requiring specific molecular machinery. Our cell-free system provides an important tool for further molecular characterization of chromatin decondensation and its coordination with concomitant processes. [Display omitted] •A cell-free assay reconstitutes mitotic chromatin decondensation•Chromatin decondensation requires ATP and GTP hydrolysis•RuvB-like ATPases and their ATPase activity function in chromatin decondensation•Both RuvBL1 and RuvBL2 can independently promote chromatin decondensation How mitotic chromosomes decondense to establish functional interphase chromatin at the end of mitosis remains ill defined. Using a cell-free system that recapitulates chromatin decondensation in vitro, Magalska et al. identify RuvB-like ATPases as crucial decondensation factors, demonstrating that decondensation is an active process with dedicated molecular machinery.