Alternative splicing generates isoforms of human neuron-derived orphan receptor-1 (NOR-1) mRNA

Neuron-derived orphan receptor-1 (NOR-1) is a novel member of the Nur77/NGFI-B subfamily within the nuclear receptor superfamily. Recently, several proteins closely related to NOR-1 have been described. To elucidate the relationships between NOR-1 and these closely related proteins, we analyzed the human NOR-1 gene and its transcripts by molecular cloning. We identified two variant NOR-1 transcripts in human skeletal muscles. One variant has a different 5'-untranslated region, and the other lacks C-terminal amino acid sequences corresponding to the putative ligand binding domain. These variant sequences share the common exon-intron boundary with NOR-1 mRNA, suggesting that they were generated from a single gene by alternative splicing, with the divergent points conserved between the rat and human. We also examined the promoter activities of the 5'-flanking regions of the two NOR-1 transcripts (NOR-1alpha and NOR-1beta mRNAs) by luciferase gene transfection. We demonstrated that the 5'-flanking region of the previously described NOR-1 gene, which has characteristics of a promoter found in housekeeping genes, showed potent promoter activity although the promoter for NOR-1beta mRNAs could not be determined.