ALTERED DNA-BINDING SPECIFICITY MUTANTS OF EKLF AND SP1 SHOW THAT EKLF IS AN ACTIVATOR OF THE BETA-GLOBIN LOCUS-CONTROL REGION IN-VIVO

The locus control region of the beta-globin cluster contains five DNas e I hypersensitive sites (5'HS1-5) required for locus activation. 5'HS 3 contains six G-rich motifs that are essential for its activity. Memb ers of a protein family, characterized by three zinc fingers highly ho mologous to those found in transcription factor Sp1, interact with the se motifs. Because point mutagenesis cannot distinguish between family members, it is not known which protein activates 5'HS3. We show that the function of such closely related proteins can be distinguished in vivo by matching point mutations in 5'HS3 with amino acid changes in t he zinc fingers of Sp1 and EKLF. Testing their activity in transgenic mice shows that EKLF is a direct activator of 5'HS3.