Interaction of nuclear factors with multiple sites in the somatic cytochrome c promoter. Characterization of upstream NRF-1, ATF, and intron Sp1 recognition sequences.

The rat somatic cytochrome c promoter is resolved into a mosaic of cis-acting upstream and intron elements required for maximal activity. Mutations in each diminished cytochrome c promoter activity and eliminated the specific binding of cognate nuclear factors. Among these is the recognition sequence for a nuclear factor designated NRF-1 (nuclear respiratory factor 1) also found in the upstream regions of several other nuclear genes whose products function in the mitochondria. The NRF-1 site was tightly coupled to a second functionally independent element (region I), and together these sites constitute a major determinant of cytochrome c expression. In addition to these novel sequence elements, the promoter also contained recognition sites for the common transcriptional activators ATF and Sp1. A potent promoter element within the first intron consisted of two adjacent Sp1 binding sites. Point mutations in the first site eliminated the promoter activity of the element as well as Sp1 binding to both sites. An ATF recognition sequence in the upstream promoter was identical to an authentic cyclic AMP (cAMP) responsive element in stimulating promoter activity and in conferring a cAMP response upon a heterologous promoter. These promoter elements and their cognate nuclear factors likely contribute to the housekeeping function of cytochrome c and to the coordinate modulation of respiratory gene expression according to cellular energy demands.