Abstract
In vitro mutagenesis of a 61-base-pair DNA sequence element that is necessary for induction of the c-fos proto-oncogene by growth factors revealed that a small region of dyad symmetry within the sequence element is critical for c-fos transcriptional activation. The same c-fos dyad symmetry element was found to bind a nuclear protein in vitro, causing a specific mobility shift of this c-fos regulatory sequence. An analysis of insertion and deletion mutants established a strict correlation between the ability of the dyad symmetry element to promote serum activation of c-fos transcription and in vitro nuclear protein binding. These experiments suggest that the DNA mobility shift assay detects a nuclear protein that mediates growth factor stimulation of c-fos expression. In vitro competition experiments indicate that the c-fos regulatory factor also binds to sequences within another growth factor-inducible gene, the beta-actin gene.