CTCF-YY1 co-bound regions associate with CpG islands. (A) The fraction of overlapping CTCF- and YY1-bound regions in H.sap, P.tro, P.pyg, and P.ham LCLs. (B) The fraction of CTCF-only, CTCF-YY1 and YY1-only binding events overlapping CpG islands across species. (C) The fraction of CTCF-only (C), CTCF-YY1 (C + Y) and YY1-only (Y) binding events overlapping CpG island transcription start sites (TSS) across species. Error bars represent standard error of the mean among four species. *P < 0.05, Wilcoxon rank-sum test, C versus C + Y.