A subset of genes encoding proteostasis-associated proteins are directly regulated by Myb in both mouse HSC and a human hematopoietic progenitor line. (A) Functional enrichment of the subset of mouse Myb insufficiency–responsive genes where their human homologs are direct target genes of MYB. Results from Wikipathways (upper panel) and KEGG pathway (lower panel) are shown. (B) A subset of Myb insufficiency–responsive genes are direct target genes of MYB in K562 cells. Left panels: UCSC tracks showing MYB occupancy at the PSMB1, PSMB3, and PSMG3. In addition to the K562 ChIP-seq tracks, we incorporated H3K27Ac tracks (accession ID: ENCFF117MIF) from the MEL mouse cell line, which is described as analogous to K562 cells in the ENCODE database. To make the MEL cell line–derived H3K27Ac ChIP-seq peaks compatible with human hg19 coordinates, we used the UCSC liftOver tool²⁶ before uploading it to the MYB UCSC session and visualizing the tracks using the UCSC genome browser.²⁷ Right panels: expression profiles of PSMB1, PSMB3, and PSMG3, respectively, in K562 cells after small interfering RNA knockdown of MYB and rescue by the transient expression of 3✕TY1-MYB. (C) Quantitative PCR of RNA expression in Myb^+/+:CreER^T2:mTmG and Myb^+/F:CreER^T2:mTmG sorted GFP+ KSL cells 24 hours after deletion. Values represent the mean expression plotted as 2^−ΔCT with SEM. n = 4 P = .047. SEM, standard error of the mean.