Nur77 (also designated NGFI-B), Nurr1 (Nur-related factor 1), and NOR-1 (neuron-derived orphan receptor 1) constitute the NGFI-B subfamily within the nuclear receptor superfamily. Ligands for these protein have not been identified, and, therefore, they are designated “orphan nuclear receptors”. Genes of the NGFI-B subfamily are classified as immediate-early genes, which are induced rapidly, but transiently, in response to a variety of stimuli. They have been implicated in cell proliferation, differentiation, and apoptosis. The human NOR-1 gene maps to chromosome 9q, and encodes a protein which is expressed in heart, skeletal muscle, thymus, and spleen as well as in brain, where it is developmentally regulated. There-fore, NOR-1 may be involved in regulating neural differentiation. The NOR-1 gene also undergoes chromosomal translocation with the EWS gene to produce a protein thought to affect pre-mRNA splicing.