An enhancer in the c-mos locus binds a nuclear factor 1-like protein.

We recently identified a DNA sequence element located in the rat c-mos protooncogene which fulfills operational criteria for enhancers, increasing transcription from a heterologous promoter in fibroblasts over large distances and in an orientation-independent manner. Here we report that three mouse nuclear proteins bind to the enhancer. Several lines of evidence indicate that one is a Nuclear Factor 1 like activity. Oligonucleotide-directed mutagenesis of the NF-1 binding site destroys binding of the protein, but leaves enhancer activity unaffected. Tumor growth factor-beta, which was shown to exert a stimulatory effect on the alpha 2(I) collagen promoter via its NF-1 binding site, has no effect on the activity of the enhancer. Thus, the NF-1 binding site of the c-mos enhancer is not essential for its activity in fibroblasts.