Structure, mapping and expression of a human NOR-1 gene, the third member of the Nur77/NGFI-B family

We identified a human homologue of NOR-1 (neuron-derived orphan receptor) from the fetal brain. There are two transcripts for human NOR-1, encoding 626 amino acid residues with a calculated molecular mass of 68 kDa. The high homology between hNOR-1, mNur77/rNGFI-B/hTR3, and mNurr1/rRNR-1/hNOT indicated that these three orphan receptors form a distinct subfamily within the steroid/thyroid receptor superfamily. Human NOR-1 mRNA was detected in the adult heart and skeletal muscle as well as in the fetal brain, indicating that its expression is not restricted to events that occur during neural development. The hNOR-1 gene is more than 35 kilobases long and interrupted by seven introns. The exon-intron structure of the gene is generally conserved when compared with the steroid/thyroid receptor superfamily and is remarkably similar to that of the Nur77/NGFI-B genes. This suggests that the Nur77/NGFI-B family has evolved from a common ancestral gene. Fluorescence in situ hybridization (FISH) revealed that the gene is located on chromosome 9q.