DNase I- and micrococcal nuclease-hypersensitive sites in the human apolipoprotein B gene are tissue specific

We have mapped the DNase I- and micrococcal nuclease-hypersensitive sites present in the 5' end of the human apolipoprotein B (apo-B) gene in nuclei from cells expressing or not expressing the gene. Four DNase I-hypersensitive sites were found in nuclei from liver-derived HepG2 cells and intestine-derived CaCo-2 cells, which express the apo-B gene, but not in HeLa cells, which do not. These sites are located near positions -120, -440, -700, and +760 base pairs relative to the transcriptional start site. Undifferentiated CaCo-2 cells exhibited another site, near position -540. Six micrococcal nuclease-hypersensitive sites were found in nuclei from HepG2 and CaCo-2 cells, but not in HeLa cells or free DNA. These sites are located near positions -120, -390, -530, -700, -850, and +210. HepG2 cells exhibited another site, near position +460. Comparison of the DNA sequence of the 5' flanking regions of the human and mouse apo-B genes revealed a high degree of evolutionary conservation of short stretches of sequences in the immediate vicinity of each of the DNase I- and most of the micrococcal nuclease-hypersensitive sites.