Mapping nucleosome resolution chromosome folding in yeast by Micro-C

We describe a Hi-C based method, Micro-C, in which micrococcal nuclease is used instead of restriction enzymes to fragment chromatin, enabling nucleosome resolution chromosome folding maps. Analysis of Micro-C maps for budding yeast reveals abundant self-associating domains similar to those reported in other species, but not previously observed in yeast. These structures, far shorted than topologically-associating domains in mammals, typically encompass one to five genes in yeast. Strong boundaries between self-associating domains occur at promoters of highly transcribed genes, and regions of rapid histone turnover that are typically bound by the RSC chromatin-remodeling complex. Investigation of chromosome folding in mutants confirms roles for RSC, “gene looping” factor Ssu72, Mediator, H3K56 acetyltransferase Rtt109, and N-terminal tail of H4 in folding of the yeast genome. This approach provides detailed structural maps of a eukaryotic genome and our findings provide insights into the machinery underlying chromosome compaction. Overall design: Chromatin is fragmented by Mnase, subsequenct nucleosomal end repair, and a modified two-step method for purfiying ligation products. Using Illumina paired-end sequencing maps Micro-C library and generates nucleosome resolution contact maps. The readme.txt file contains additional description of how each processed data file was generated.