Transcriptional repressor. Dimerization is required for DNA-binding. At stage 15, expressed in the anterior/superior eye field and the caudal branchial arch. At later stages, expression persists in the retina and in the caudal branchial arch. Expressed in the pronephros and the tip of the tail. Beginning with stage 35, expression in the brain is localized to distinct subdomains of the anterior prosencephalon, the medial mesencephalon and to lateral domains of the hindbrain. First expressed weakly at mid-gastrula (stage 11) but expression becomes prominent at stage 15. The leucine-zipper is required for dimerization and transcriptional repression.