The +42-kb enhancer is a myeloid-specific CEBPA transcriptional activator. (A-B) The +42-kb and +9-kb enhancer were cloned 3′ of a luciferase reporter gene under the control of the full canonical CEBPA promoter. Results are presented as fold change of the +42-kb enhancer in combination with the CEBPA promoter (blue = myeloid; red = lymphoid; green = CEBPA⁺ nonhematopoietic; orange = CEBPA⁻ nonhematopoietic cell lines) relative to CEBPA promoter alone (gray). (C) gRNA for the CRISPR/Cas9 system were designed to flank the p300 and TF-binding sites within the +42-kb enhancer. Single-cell clones were generated and genotyped using a PCR strategy. (D-E) WT clones (n = 6) and homozygous clones (n = 9) were selected and qPCR for CEBPA mRNA expression and for CEBPG was conducted. Statistical significance to compare mRNA expression levels between WT and homozygous clones for both genes under investigation, was carried out using the 2-tailed Student’s t test. ***P < .0001; N.S., not significant.