The human DNA binding factor GRF-1, which associates with the promoter region of the glucocorticoid receptor gene (hGR gene), is a repressor of glucocorticoid receptor transcription. The GRF-1 cDNA was cloned using polyclonal antibodies against the purified protein. The deduced amino acid sequence from the cDNA sequences show the presence of three sequence motifs characteristic of a zinc finger and one motif suggestive of a leucine zipper in which 1 cysteine is found instead of all leucines.

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... GRF-i expressed in COS-1 cells has a molecular weight of 95,000 and enhances the homologous down-regulation of wildtype hGR gene expression. Biochemical analysis suggests that GRF-1 interaction is sequence specific and that transcriptional efficacy of GRF-1 is regulated through its interaction with specific sequence motif, namely 5"GAAGGAGGTAGCGAGAAAAGAAACTG-GAGAAACTCGGT.GG-3'. The GRF-1 mRNA is 6.5 kilobases long in rat liver and human MCF-7 cells, and its level is regulated by glucocorticoids. Steroid receptors are trans-acting protein factors that interact with their cognate ligands and bind to specific DNA sequences known as steroid-responsive elements (1). The interaction between steroid receptors and responsive elements of the target gene have been studied in detail to understand the mechanism of hormone-regulated transcription (2-6). The cellular glucocorticoid receptor concentration is modulated by a number of factors, including glucocorticoids, which downregulate their own cellular receptor concentration (7-13). Using cloned human glucocorticoid receptor gene fragments fused to bacterial chloramphenicol acetyltransferase, we have demonstrated that the sequences responsible for homologous down-regulation of the human GR' gene (nucleotide sequence of human glucocorticoid receptor gene GenBank accession No. M73050) lie between -245 to -750 nucleotides 5' to the mRNA start site ( 14 ). This region is characterized by the