PT - JOURNAL ARTICLE AU - Johann Holzmann AU - Antonio Z. Politi AU - Kota Nagasaka AU - Merle Hantsche-Grininger AU - Nike Walther AU - Birgit Koch AU - Johannes Fuchs AU - Gerhard Dürnberger AU - Wen Tang AU - Rene Ladurner AU - Roman R. Stocsits AU - Georg A. Busslinger AU - Bela Novak AU - Karl Mechtler AU - Iain F. Davidson AU - Jan Ellenberg AU - Jan-Michael Peters TI - Absolute quantification of cohesin, CTCF and their regulators in human cells AID - 10.1101/560425 DP - 2019 Jan 01 TA - bioRxiv PG - 560425 4099 - http://biorxiv.org/content/early/2019/02/27/560425.short 4100 - http://biorxiv.org/content/early/2019/02/27/560425.full AB - The organisation of mammalian genomes into loops and topologically associating domains (TADs) contributes to chromatin structure, gene expression and recombination. Loops and TADs are formed by cohesin and positioned by CTCF. In proliferating cells, cohesin also mediates sister chromatid cohesion, which is essential for chromosome segregation. Current models of chromatin folding and cohesion are based on assumptions of how many cohesin and CTCF molecules organise the genome. Here we have measured absolute copy numbers and dynamics of cohesin, CTCF, NIPBL, WAPL and sororin by mass spectrometry, fluorescence-correlation spectroscopy and fluorescence recovery after photobleaching in HeLa cells. In G1-phase there are ~245,000 cohesin complexes, of which ~139,000 are on chromatin. Comparison with chromatin immunoprecipitation-sequencing data implies that some genomic cohesin and CTCF enrichment sites are unoccupied in single cells at any one time. We discuss the implications of these findings for how cohesin can contribute to genome organisation and cohesion.