Absolute quantification of cohesin, CTCF and their regulators in human cells

We have measured absolute copy numbers and dynamics of cohesin, CTCF and their regulators NIPBL, WAPL and sororin by mass spectrometry, fluorescence-correlation spectroscopy and fluorescence recovery after photobleaching in HeLa cells before and after DNA replication. Comparison of these numbers with chromatin immunoprecipitation-sequencing data implies that some genomic cohesin and CTCF enrichment sites are unoccupied in single cells at any one time. Overall design: Absolute quantification of cohesin copy number by liquid chromatography mass spectrometry and fluorescence-correlation spectroscopy.