CHARACTERIZATION OF THE NUCLEAR PROTEINS BINDING THE CACCC ELEMENT OF A GLUCOCORTICOID-RESPONSIVE ENHANCER IN THE TYROSINE AMINOTRANSFERASE GENE

The nuclear proteins which act synergistically with the glucocorticoid receptor to induce transcription of the tyrosine aminotransferase gene include factors recognizing the CACCC element. We have purified and characterized the proteins from rat liver nuclei which bind to the CACCC motif in the glucocorticoid-inducible enhancer of the gene. Three protein-DNA complexes (C1, C2, and C3) were detected in band-shift assays. The protein component of complex C1 also binds a GC motif (a Sp1 binding site) and is recognized by anti-Sp1 antiserum. The proteins forming complexes C2 and C3 have been purified by DNA-affinity chromatography and their molecular masses (75-80 kDa and 35-40 kDa, respectively) have been determined by ultraviolet cross-linking to radio-labelled DNA and SDS/PAGE. The DNA-affinity-purified C2 and C3 activities do not bind significantly to the GC motif and are not recognized by anti-Sp1 antiserum. Methylation interference analysis indicates that the nucleotides of the CACCC element bound by the C2 and C3 proteins correspond to those of the glucocorticoid-responsive enhancer which are contacted in vivo following glucocorticoid administration. Our data suggest that these proteins contribute to glucocorticoid-induced transcription of the tyrosine aminotransferase gene.