Occupation of the c-fos serum response element in vivo by a multi-protein complex is unaltered by growth factor induction

Abstract

RAPID, transient induction of the human c-fos proto-oncogene by extracellular signals requires the presence in els of the serum response element (SRE)^1,2. Two protein factors that bind to the SRE in vitro are the serum response factor (p67^SRF)^3—5 and polypeptide p62 (ref. 6). These polypeptides must interact with one another and the SRE for efficient serum induction of the c-fos gene⁶. Here we use dimethyl sulphate genomic footprinting⁷ to establish the in vivo protein contacts on the SRE and flanking sequences. In human A431 cells the patterns of protection and hyper-reactivity that we find are consistent with the presence of p67^SRF, p62, and at least one other protein immediately 3' to p67^SRF. The protein-DNA contacts we observe within the SRE are present before induction by epidermal growth factor and are unchanged during gene activation and subsequent repression. Our results indicate that a specific DNA—protein architecture may be maintained at the c-fos SRE, regardless of changes in the transcriptional state of the gene. Such established structures could be important generally in rapid transcriptional responses to extracellular signals.