Functional role of TTF‐1 binding sites in bovine thyroglobulin promoter

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Abstract
We have studied the binding of purified TTF‐1 on the bovine thyroglobulin gene promoter. DNase I footprinting experiments revealed three binding sites which corresponded in location to the A, B and C sites found in the rat thyroglobulin promoter. Mutants in the A and C regions showing reduced binding of TTF‐1, also exhibited largely decreased promoter activity in transient expression experiments in primary‐cultured dog thyrocytes. Two mutants in the B site that exhibited a reduced capacity to bind TTF‐1 also displayed a drastically affected transcriptional activity in transient assays. As in the rat, sites A and C only are critical for promoter activity, these results suggest that full occupancy of the B site is required for thyroglobulin promoter activity in the cow only.