The mechanisms for cell type specific, regulated expression of eucaryotic genes are central questions of biology. We have focused efforts on investigating the transcriptional regulation of the rat growth hormone (rGH) gene by thyroid hormone (T3). Both T3 and growth hormone are essential to the regulation of many metabolic processes in both juvenile and adult mammals. Recent evidence suggests that the verb-A oncogene is related to the thyroid hormone receptor. We have shown that transcription of the rGH gene is regulated by T3. We have identified two genetic elements responsive to thyroid hormone in rGH 5'-flanking DNA. The first of these is a T3 responsive, transcription stimulatory element, or TSE. The TSE induced a T3 dependent, transient increase in transcription similar to that found for the natural gene. The second regulatory element is a T3 responsive, transcription inhibitory element (TIE). When this element is active, T3 strongly but transiently inhibits rGH promoter activity. We propose to continue our studies of these elements by: 1) Further structural and functional mapping of the TIE; 2) Further structural and functional mapping of the TSE; 3) Physical mapping of transcription factor binding sites on the TIE and TSE gene regions; 4) Structural and structure-function analysis of the putative rat T3 receptor gene(s) (rat c-erb-A genes). We will use our putative receptor clones to study the mechanism of action of the TIE and TSE. We also will analyze the site specific DNA binding and the functional activity of the v-erb-A oncogene product in vivo and in vitro using the TIE and TSE.
