SUMMARY
Quiescence is a stress-resistant state in which cells reversibly exit the mitotic cell cycle and suspend most cellular processes. Quiescence is essential for stem cell maintenance and its misregulation is implicated in tumor formation. One of the conserved hallmarks of quiescent cells, from Saccharomyces cerevisiae to humans, is highly condensed chromatin. Here, we use Micro-C XL to map chromatin contacts at single-nucleosome resolution genome-wide to elucidate mechanisms and functions of condensed chromatin in quiescent S. cerevisiae cells. We describe previously uncharacterized chromatin domains on the order of 10-60 kilobases that in quiescent cells are formed by condensin-mediated chromatin loops. Conditional depletion of condensin prevents chromatin condensation during quiescence entry and leads to widespread transcriptional de-repression. We further demonstrate that condensin-dependent chromatin compaction is conserved in quiescent human fibroblasts. We propose that condensin-dependent condensation of chromatin represses transcription throughout the quiescent cell genome.
