Coordinate expression of c‐myc, c‐myb, and histone H4 genes in reversibly differentiating HL 60 cells

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Abstract
The expression of oncogenes c‐myc and c‐myb in human leukemic cells HL 60 was compared to the expression of histone H4 gene, known to be cell‐cycle dependent. Steady‐state levels of mRNA transcribed from these genes were determined by simultaneous hybridization of Northern transfers with four probes, and the rates of gene expression were measured by nuclear transcription (“run‐on”) assays. Expression of genes c‐myc, c‐myb and histone H4 varied coordinately and in parallel with the rates of DNA synthesis, while the rates of total and ribosomal RNA synthesis, the expression of gene c‐Haras, unrelated to proliferation of these cells, and gene p 72, a constitutively expressed human gene, were unchanged. Further, the levels of c‐myc and c‐myb mRNA but not p 72 mRNA were higher in cell populations enriched for S phase cells. Thus, transcription of genes c‐myc and c‐myb in HL 60 cells appears to be linked to DNA replication in a manner previously demonstrated for core histone gene expression.