COUP transcription factor is a member of the steroid receptor superfamily

The COUP (chicken ovalbumin upstream promoter) transcription factor (COUP-TF) exists in a number of different tissues and is essential for expression of the chicken ovalbumin gene. It binds to the ovalbumin promoter and, in conjunction with a second protein (S300-II), stimulates initiation of transcription in vitro. COUP-TF also binds specifically to the rat insulin promoter element, although the two binding sites share little sequence similarity. Here we report the isolation of a human complementary DNA clone encoding COUP-TF. Comparison of the amino-acid sequence of COUP-TF with known sequences reveals that it is a member of the steroid/thyroid hormone/vitamin receptor superfamily. Consequently, it is the first member of this family that has been shown to function in a cell-free transcription system. We conclude that this superfamily of gene regulators contains proteins which bind and activate distal promoter elements of eukaryotic genes.