DELTA-CRYSTALLIN ENHANCER-BINDING PROTEIN DELTA-EF1 IS A ZINC FINGER-HOMEODOMAIN PROTEIN IMPLICATED IN POSTGASTRULATION EMBRYOGENESIS

We investigated nuclear factors that bind to delta1-crystallin enhance r core and regulate lens-specific transcription. A nuclear factor delt aEF1, which binds to the essential element of the delta1-crystallin en hancer core, was molecularly cloned from the chicken by a southwestern method. The protein organization of deltaEF1 deduced from the cDNA se quence indicated that it has heterogeneous domains for DNA-binding, tw o widely separated zinc fingers and a homeodomain, analogous to Drosop hila ZFH-1 protein. The C-terminal zinc fingers were found to be respo nsible for binding to the delta1-crystallin enhancer core sequence. de ltaEF1 had proline-rich and acidic domains common to various transcrip tional activators. During embryogenesis, deltaEF1 expression was obser ved in the postgastrulation period in mesodermal tissues; initially, i n the notochord, followed by somites, nephrotomes and other components . The expression level changed dynamically in a tissue, possibly refle cting the differentiation states of the constituent cells. Besides mes oderm, deltaEF1 was expressed in the nervous system and the lens, but other ectodermal tissues and endoderm remained very low in deltaEF1 ex pression. Cotransfection experiments indicated that this factor acts a s a repressor of delta1-crystallin enhancer. Possession of heterogeneo us DNA-binding domains and its dynamic change of expression in embryog enesis strongly suggest that deltaEF1 acts in multiple ways depending on the cell type and the gene under its regulation.