Genes expressed in erythroid cells contain binding sites for a cell-specific nuclear factor, GF-1 (NF-E1, Eryf 1), believed to be an important transcriptional regulator. Previously we characterized murine GF-1 as a 413-amino acid polypeptide containing two cysteine-cysteine regions reminiscent of zinc-finger DNA-binding domains. By cross-hybridization to the finger domain of murine GF-1 we have isolated cDNA encoding the human homolog. Peptide sequencing of purified human GF-1 confirmed the authenticity of the human cDNA. The predicted primary sequence of human GF-1 is highly similar to that of murine GF-1, particularly in the DNA-binding region. Although the DNA-binding domains of human, murine, and chicken proteins are remarkably conserved, the mammalian polypeptides are strikingly divergent from the avian counterpart in other regions, most likely those responsible for transcriptional activation. By hybridization to panels of human-rodent DNAs we have assigned the human GF-1 locus to Xp21-11. The localization of the gene to the X chromosome has important implications for hereditary persistence of fetal hemoglobin syndromes unlinked to the beta-globin cluster and for genetic experiments designed to test the role of the factor in erythroid cell gene expression.