| Autor: |
Brooks, A R, Blackhart, B D, Haubold, K, Levy-Wilson, B |
| Zdroj: |
Journal of Biological Chemistry; April 1991, Vol. 266 Issue: 12 p7848-7859, 12p |
| Abstrakt: |
We report the identification and characterization of tissue-specific transcriptional enhancer elements that influence the expression of the human apolipoprotein B gene. A 704-base pair PstI fragment comprising sequences from the first and second introns of the human apolipoprotein B gene (positions +360 to +1064) possesses tissue-specific transcriptional enhancer elements when assayed in transient transfection experiments using either the apolipoprotein B or thymidine kinase promoter. The majority of the enhancer activity, which was observed in transcriptionally active HepG2 and CaCo-2 cells, but not in transcriptionally inactive Chinese hamster ovary or HeLa cells, was subsequently localized to a 443-base pair SmaI-PvuII fragment (positions +621 to +1064) within the second intron of the apolipoprotein B gene. Gel retention experiments demonstrated that sequence motifs within this region interact with a number of nuclear proteins from HepG2, CaCo-2, and HeLa cells. The actual sequence elements that bound to nuclear proteins from HepG2 cells were identified by DNase I footprinting. Deletion experiments were performed to distinguish those protein-binding regions involved in the enhancer effect. Our data demonstrate that sequences between positions +806 and +940 are essential for this enhancer activity. This segment contains one large 97-base pair footprint, whose sequence has been conserved between the human and mouse genes. Binding sites for the liver-specific transcription factors HNF-1 and HNF-3 are present within this footprint. |
| Databáze: |
Supplemental Index |
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