Transcription factor RFX1 helps control the promoter of the mouse ribosomal protein-encoding gene rpL30 by binding to its alpha element.

The factor that binds to the most upstream element (alpha) of the mouse rpL30 promoter was identified as RFX1, a novel 105-kDa protein that recognizes an important element of MHC class-II promoters. Identification was based on competition between rpL30 alpha and an RFX1-binding site for nuclear protein complex formation and on the ability of RFX1 antibody to supershift the electrophoretic mobility of the DNA-protein complexes. A mutation in the alpha-element that abolished its interaction with RFX1 reduced rpL30 promoter activity to about 43% of the wild-type level, indicating that RFX1 plays an important role in determining the strength of the rpL30 promoter. A search of a eukaryotic promoter database revealed candidate RFX1-binding sites in a variety of other promoters, suggesting that this protein may be implicated in the transcriptional regulation of a wide variety of genes.