Characterization of the rat LDL receptor 5'-flanking region.

A 1.5-kb genomic DNA fragment corresponding to the 5'-flanking region of the rat LDL receptor gene was cloned and putative regulatory regions were identified. A major transcription start site was identified at -154 bp relative to the ATG translation initiation codon, within a region containing two thyroid hormone response element half-site motifs (2H-TRE). Binding of thyroid hormone receptors alpha and beta1 to this element was demonstrated. Mutations within this 2H-TRE region abolished basal transcription levels of the rat LDL receptor gene. Reporter gene studies indicated that the promoter region between -300 and -200 bp, which contains one sterol response element (SRE) and two specificity protein-1 sites (Sp1) sites, is crucial for basal transcription of the rat LDL receptor gene. The functionality of the SRE motif was confirmed using electrophoretic mobility shift assays and reporter gene studies.