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A mutational analysis of the rat cytochrome c oxidase subunit IV (RCO4) promoter region revealed the presence of a major control element consisting of a tandemly repeated pair of binding sites for a nuclear factor from HeLa cells. This factor was designated NRF-2 (nuclear respiratory factor 2) because a functional recognition site was also found in the human ATP synthase beta-subunit gene. Deletion or site-directed point mutations of the NRF-2 binding sites in the RCO4 promoter resulted in substantial loss of transcriptional activity, and synthetic oligomers of the NRF-2 binding sites from both genes stimulated a heterologous promoter when cloned in cis. NRF-2 binding and transcriptional activation required a purine-rich core sequence, GGAA. This motif is characteristic of the recognition site for a family of activators referred to as ETS domain proteins because of the similarity within their DNA-binding domains to the ets-1 proto-oncogene product. NRF-2 recognized an authentic Ets-1 site within the Moloney murine sarcoma virus long terminal repeat, and this site was able to compete for NRF-2 binding to the RCO4 promoter sequence. In addition, a single polypeptide of 55 kDa was detected following cross-linking of a partially purified NRF-2 fraction to RCO4, the human ATP synthase beta subunit, or Moloney murine sarcoma virus binding sites. However, in contrast to Ets-1, which appears to be exclusive to lymphoid tissues, NRF-2 has the broad tissue distribution expected of a regulator of respiratory chain expression.
Virbasius et al. (Fri,) studied this question.