Colocalization of CTCF and H3K9me3 at the IGF2BP1 locus. Array-based chromatin immunoprecipitation (ChIP-chip) data for both CTCF and histone H3 trimethylated at lysine 9 (H3K9me3) identify candidate loci for analysis of monoallelic expression. (A) Depiction of the IGF2BP1 gene with specific SNPs examined in this study (arrows). (B) Close-up portion of the locus with tracks for CTCF enrichment (top track) and H3K9me3 association (bottom track) near SNP site rs11870560. The ChIP-chip data are displayed using the UCSC Genome Browser. DNA derived from CTCF ChIP experiments was analyzed by using microarrays with hybridization probes spaced 100 bp apart. The higher resolution of the H3K9me3 ChIP-chip data is due to the use of condensed array sets that tiled through all of the CTCF-positive regions with probes overlapping each other by 12 nt.