Nuclear respiratory factor 1 (NRF-1) is a transcription factor that acts on nuclear genes encoding respiratory subunits and components of the mitochondrial transcription and replication machinery. Here we describe the isolation and characterization of the human gene encoding NRF-1. The human genomic sequences detected with NRF-1 cDNA probes at high stringency are all contained within seven overlapping recombinant lambda clones. The NRF-1 gene encompassed by these recombinants spans approximately 65 kilobases (kb) and has 11 exons and 10 introns that range in size from 0.8 to 15 kb. A rapid amplification of cDNA ends-polymerase chain reaction product containing the 5'-terminus of the NRF-1 cDNA has two exons from the 5'-untranslated region and terminates at a major transcription initiation site identified by S1 nuclease mapping. A genomic fragment containing a portion of the 5'-terminal exon and an additional 1 kb upstream had a functional promoter that was active in transfected COS cells, HeLa cells, and L6 myoblasts. The transcription initiation site utilized by the transfected promoter corresponded to that used by the endogenous gene in vivo. NRF-1 mRNA was expressed at very low levels in rat tissues compared with cytochrome c and, unlike cytochrome c, was most abundantly expressed in lung and testis. The NRF-1 gene was localized to human chromosome 7 by analysis of DNA from a panel of human-hamster cell hybrids with human-specific NRF-1 polymerase chain reaction primers. This assignment was further refined to 7q31 by cohybridization of NRF-1- and chromosome 7-specific probes to human metaphase chromosomes. These analyses should be useful in evaluating the potential role of NRF-1 in mitochondrial diseases resulting from defects in the nuclear control of mitochondrial function.