TRANSCRIPTION FROM THE THYROID HORMONE-DEPENDENT PROMOTER OF THE XENOPUS-LAEVIS THYROID-HORMONE RECEPTOR BETA-A GENE REQUIRES A NOVEL UPSTREAM ELEMENT AND THE INITIATOR, BUT NOT A TATA BOX

The thyroid hormone receptor (TR) beta genes in Xenopus laevis are reg ulated by thyroid hormone in all organs of an animal during metamorpho sis. This autoregulation appears to be critical for systematic transfo rmations of different organs as a tadpole is transformed into a frog. To understand this autoregulation, we have previously identified a thy roid hormone response element in the hormone-dependent promoter of the X. laevis TR beta A gene. We report here the detailed characterizatio n of the promoter. We have now mapped the transcription start site and demonstrated the existence of an initiator element at the start site critical for promoter function. More important, our deletion and mutat ional experiments revealed a novel upstream DNA element that is locate d 125 base pairs upstream of the start site and that is essential for active transcription from the promoter Promoter reconstitution experim ents showed that this novel element does not function as an enhancer, but acts as a core promoter element, which, together with the initiato r, directs accurate transcription from the promoter. Finally, we provi de evidence for the existence of a protein(s) that specifically recogn izes this element, Our studies thus demonstrate that the TR beta A pro moter has a unique organization consisting of an initiator and a novel upstream promoter element. Such an organization may be important for the ubiquitous but tissue-dependent temporal regulation of the gene by thyroid hormone during amphibian metamorphosis.