We investigated nuclear factors that bind to δ1-crystallin enhancer core and regulate lens-specific transcription. A nuclear factor δEF1, which binds to the essential element of the δ1-crystallin enhancer core, was molecularly cloned from the chicken by a southwestern method. The protein organization of δEF1 deduced from the cDNA sequence indicated that it has heterogeneous domains for DNA-binding, two widely separated zinc fingers and a homeodomain, analogous to Drosophila ZFH-1 protein. The C-terminal zinc fingers were found to be responsible for binding to the δ1-crystallin enhancer core sequence. δEF1 had proline-rich and acidic domains common to various transcriptional activators. During embryogenesis, δEF1 expression was observed in the postgastrulation period in mesodermal tissues; initially, in the notochord, followed by somites, nephrotomes and other components. The expression level changed dynamically in a tissue, possibly reflecting the differentiation states of the constituent cells. Besides mesoderm, δEF1 was expressed in the nervous system and the lens, but other ectodermal tissues and endoderm remained very low in δEF1 expression. Cotransfection experiments indicated that this factor acts as a repressor of δ1-crystallin enhancer. Possession of heterogeneous DNA-binding domains and its dynamic change of expression in embryogenesis strongly suggest that EF1 acts in multiple ways depending on the cell type and the gene under its regulation.