Product of the cellular oncogene, c-fos, observed in mouse and human tissues using an antibody to a synthetic peptide.

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Abstract
The transforming gene of the osteosarcoma‐producing FBJ murine sarcoma virus, v‐fos, is homologous to a normal cellular gene, c‐fos, in vertebrate species. Transcripts from the c‐fos proto‐oncogene accumulate to very high levels in late gestational mouse and human extra‐embryonic tissues. We now report that these RNA transcripts are translated in these tissues. Rabbits were immunized with a synthetic peptide whose sequence is common to both c‐fos and v‐fos. After affinity purification on an immunosorbent containing the fos peptide (a nonapeptide), the antibody reacted with a component(s) in nuclei in sections of human and murine tissues and immunoprecipitated the v‐fos gene product (p55) and a cellular protein of 39 kd (p39, complexed with fos) from lysates of metabolically‐labelled virally transformed cells. Crude extracts of normal tissues contained major anti‐fos‐reactive proteins in the range of 55‐60 kd as shown by protein blot analysis. Indirect immunofluorescence and immunoperoxidase staining showed that in addition to strong immunoreactive component(s) in the nuclei of extra‐embryonic tissues of human and mouse, weaker reactions are detectable in all normal fetal and adult tissues tested. This demonstrates that fos‐reactive protein is expressed in a wide variety of cells and tissues.