δEF1 (δ-crystallin/E2-box factor 1) is a widely distributed repressor of transcription which binds at the E2-box sequence, CACCTG. It carries seven zinc fingers (Zf) in two clusters and a homeodomain in the middle as potential DNA-binding domains. We cloned the genomic gene encoding chicken δEF1 and analyzed its organization. The gene consisted of nine exons, the N-proximal Zf were encoded by exons 5 through 7, and the C-proximal Zf by exons 8 and 9. Exon 7 also coded for the large middle portion of the protein including the homeodomain. Promoter analysis and RNase-protection assay indicated that the gene is driven by a G + C-rich promoter without a TATA box, and the transcription start points (tsp) cluster around 20 bp from the start codon located in exon 1. cDNA and genomic sequences of the mouse δEF1 were cloned and compared with the chicken sequence. The deduced amino acid (aa) sequence was highly conserved between the chicken and mouse δEF1, not only in DNA-binding motifs but also in other blocks (78% overall aa identity). More recently reported DNA-binding proteins, AREB6 (human), ZEB (human) and BZP (hamster), were attributed to homologues of δEF1, among which only AREB6 represented a full-length sequence. It was also indicated that rodent δEF1 lacked exon 3.
- chicken δ-crystallin enhancer
- E2 box
- G + C-rich promoter
- zinc finger