ISOLATION AND CHARACTERIZATION OF THE CDNA-ENCODING BKLF TEF-2, A MAJOR CACCC-BOX-BINDING PROTEIN IN ERYTHROID-CELLS AND SELECTED OTHER CELLS/

CACCC boxes are among the critical sequences present in regulatory ele ments of genes expressed in erythroid cells, as well as in selected ot her cell types. While an erythroid cell-specific CACCC-box-binding pro tein, EKLF, has been shown to be required in vivo for proper expressio n of the adult beta-globin gene, it is dispensable for the regulation of several other globin and nonglobin erythroid cell-expressed genes. In the work described here, we searched for additional CACCC-box trans cription factors that might be active in murine erythroid cells. We id entified a major gel shift activity (termed BKLF), present in yolk sac and fetal liver erythroid cells, that could be distinguished from EKL F by specific antisera. Through relaxed-stringency hybridization, we o btained the cDNA encoding BKLF, a highly basic, novel zinc finger prot ein that is related to EKLF and other Kruppel-like members in its DNA- binding domain but unrelated elsewhere. BKLF, which is widely but not ubiquitously expressed in cell lines, is highly expressed in the midbr ain region of embryonic mice and appears to correspond to the gel shif t activity TEF-2, a transcriptional activator implicated in regulation of the simian virus 40 enhancer and other CACCC-box-containing regula tory elements. Because BKLF binds with high affinity and preferentiall y over Sp1 to many CACCC sequences of erythroid cell-expressed genes, it is likely to participate in the control of many genes whose express ion appears independent of the action of EKLF.