Previous studies have examined the arrangement of regulatory elements along the apolipoprotein B (apoB) promoter region (-3067 to +940) and a promoter fragment extending from nucleotides -150 to +124 has been demonstrated to be essential for transcriptional activation of the apoB gene in hepatic and intestinal cells. It has also been shown that transcriptional activation of apoB requires a synergistic interaction between hepatic nuclear factor-4 (HNF-4) and CCAAT/ enhancer-binding protein α

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... BPα) transcription factors. Here, we have examined the hypothesis that HNF-4 factor binding to DNA may induce a DNA helix bend, thus facilitating the communication with a C/EBPα factor located one helix turn from this HNF-4 factor in the apoB promoter. A gel electrophoretic mobility shift assay using wild type double-stranded oligonucleotides or modified wild type duplex oligonucleotides with 10 nucleotides inserted between HNF-4 and C/ EBPα factor motifs showed similar retarded complexes, indicating that HNF-4 and C/EBPα factors interact independently of the distance between binding sites. However, when only one base, a thymidine, was inserted at the -71 position of the apoB promoter, the complex shift was completely abolished. In conclusion, these results regarding the study of the mechanisms involving the interaction between HNF-4 and C/EBPα factors in the apoB promoter suggest that the perfect 5'-CCCTTTGGA-3' motif is needed in order to facilitate the interaction between the two factors.