Abstract
A set of proteins antigenically related to the c-fos protein (Fos) are induced by serum in fibroblasts. To isolate cDNA clones of genes encoding such proteins, a lambda gt11 expression cDNA library constructed from serum-stimulated rat fibroblasts was screened with antibodies raised against a hydrophilic region (amino acids 127 to 152) of Fos. One of the positive clones identified, termed fra-1 (Fos-related antigen) was characterized. It encoded a protein that shared several regions of extensive amino acid homology with Fos (including the region that showed similarity to both the yeast GCN4 regulatory protein and the protein encoded by the jun oncogene), although its nucleotide sequence was considerably diverged from that of the c-fos gene. Only a subset of the agents and conditions that activated c-fos also induced fra-1. Induction of fra-1 expression following serum stimulation was delayed compared with that of c-fos. However, like c-fos, fra-1 was induced rapidly by serum in the presence of protein synthesis inhibitors. Thus, a family of Fos-related, inducible genes are involved in the cellular immediate-early transcriptional response to extracellular stimuli.