Updated project metadata. To obtain a comprehensive and quantitative view on MBD2 vs MBD3-NuRD complex stoichiometry, we performed biotin co-immunoprecipitations in Mbd3 KO ES cells expressing either biotin-tagged MBD2a or MBD3a and identified known NuRD complex members using label-free mass spectrometry (Supplementary Fig. 8b-c). We then calculated the intensity-based absolute quantification (iBAQ) values of the most predominant and statistically significant MBD-interacting proteins in both cell lines, which can be used to estimate the relative abundance. While we observe very similar complex composition between MBD2a-NuRD and MBD3a-NuRD, peptides shared between SALL1-4 proteins show a preferred interaction with the MBD2a-NuRD complex.