BRD1 and HBO1 coregulate erythroid genes. (A) ChIP-chip analysis of BRD1 and HBO1 binding in K562 cells. A ChIP-chip analysis was performed in K562 cells coexpressing 3xFlag-BRD1 and HA-HBO1 by use of anti-Flag and HA antibodies. Fold enrichment > 4 was judged as positive. The number of genes in each category of the Venn diagram is indicated. (B) Average BRD1 and HBO1 binding was depicted in the promoter regions (from −6 kb to +6 kb relative to the transcription start site) of all genes in the ChIP-on-chip analysis. The dotted line represents the normalized average signal over the entire chip. (C) Graph of the correlation of expressed genes in K562 cells in terms of the degree of BRD1 or HBO1 binding. Gene expression profiles of K562 cells examined with microarrays were used to judge the transcriptional status of the BRD1- or HBO1-occupied genes identified in the ChIP-chip analysis. The percentage of probes that produced “PRESENT” signals in the microarray analysis was plotted against the BRD1 or HBO1 binding detected in the ChIP-on-chip analysis. (D) ChIP-on-chip signals in the GATA1 and TAL1 promoter regions. Blue columns indicate the probes with no signals. The GATA1 and TAL1 gene structures and the location of the primer sets are depicted. (E) ChIP analyses at the GATA1 and TAL1 loci. The binding of BRD1 and HBO1 to the indicated regions of the GATA1 and TAL1 genes was determined by ChIP and site-specific real-time PCR. The relative amount of immunoprecipitated DNA is depicted as a percentage of input DNA. The data are shown as the mean ± SE for triplicate PCRs. The ALB promoter served as a negative control. Pro indicates promoter; and Down, 3 kb downstream from the polyadenylation site.