Nkx6.1 (gene symbol NKX6A), a new member of the NK homeobox gene family, was recently identified in rodent pancreatic islet beta-cell lines. The pattern of expression suggested that this gene product might be important for control of islet development and/or regulation of insulin biosynthesis. We now report cloning of human NKX6A, characterization of its genomic structure, and its chromosomal localization. The predicted protein of human NKX6A contained 367 amino acids and had 97% identity to the hamster protein. The highly conserved NK decapeptide and homeodomain regions were identical between human and hamster, suggesting functional importance of these domains. The coding region spanned approximately 4.8 kb and was composed of three exons. The gene was localized to four CEPH "B" yeast artificial chromosome clones (914B4, 951G9, 981D6, and 847B3), and a nearby polymorphic marker (D4S1538) on chromosome 4 was identified < 1270 kb from the gene. Using fluorescence in situ hybridization, we also determined that NKX6A maps to 4q21.2-q22.