COORDINATE EXPRESSION AND DISTINCT DNA-BINDING CHARACTERISTICS OF THE4 EGR-ZINC FINGER PROTEINS IN JURKAT T-LYMPHOCYTES

The Early Growth Response Genes (EGR-1 to AT133/EGR-4) encode a family of proteins that are composed of three homologous consecutive zinc fi ngers of the Cys(2)-His(2) type and different flanking sequences. Upon growth stimulation of resting cells the four EGR-genes are simultaneo usly transcribed. We have analyzed the expression of the four EGR-prot eins in Jurkat T cells and show by Western blot analysis that the four :EGR-proteins are coordinately induced upon treatment with a combinat ion of PHA and PMA,,4s the individual proteins are reported to bind to identical target sequences, we have analyzed the DNA-binding of the n ative proteins. Using nuclear extract in which we have demonstrated ex pression of all four EGR-proteins, only EGR-1, but no other member of this protein family is found to bind to the EGR-consensus site (GCG GG G GCG). In addition, DNA-binding of both native EGR-1 and of recombina nt EGR-1 and AT133/EGR-4 proteins expressed in insect cells was analyz ed. This comparison revealed distinct binding properties of recombinan t EGR-1 and AT133/EGR-4 to oligonucleotides that include the EGR-conse nsus sites. The distinct binding affinities suggest chat in vivo EGR-p roteins bind to different target sequences and that each EGR-protein r egulates distinct target genes. This is underlined by demonstrating th at EGR-1 but not AT133/EGR-4 binds to a related G-rich promoter elemen t with the sequence GGG GTG GGG. This G-rich sequence serves as an ove rlapping binding site for the two zinc finger proteins EGR-1 and Spl. As similar overlapping binding sites for EGR-1 and Spl have been ident ified In several human and mouse gene promoters, we raise the question whether the Spl binding sites described in a large number of eukaryot ic gene promoters also represent binding sites for EGR-1.