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Two binding sites for thyroid transcription factor 1 (TTF-1) determine the activity of the bovine thyroglobulin gene upstream enhancer element

par Hobertus, Christiane ;Christophe, Daniel
Référence Molecular and Cellular Endocrinology, 149, page (79-84)
Publication Publié, 1999

Article révisé par les pairs

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Résumé :

A thyroid-specific enhancer element located upstream from the bovine thyroglobulin gene had been shown to contain three contiguous regions that are protected by thyroid transcription factor 1 (TTF-1) in footprinting experiments in vitro. The functional relevance of the individual TTF-1 binding sites was investigated in a transient assay in primary cultured thyrocytes. Using reporter constructs containing synthetic oligonucleotides overlapping the protected sequences we were able to show that only two out of the three TTF-1 binding sites exhibit transcription enhancing activity. Within the context of the complete enhancer sequence, the central 'inactive' TTF-1 site could be deleted whithout any consequence on the activity of the enhancer in the assay, whereas the presence of both terminal 'active' TTF-1 sites had previously been shown to be strictly required for enhancer function. Our results thus show that the activity of the bovine thyroglobulin upstream enhancer relies on the presence of a pair of TTF-1 binding sites separated by about 30 bp. These results also emphasize the need to assess experimentally the functional relevance of TTF-1 binding sites identified in footprinting experiments.