Characterization of a 142-bp fragment of the murine c- fos oncogene promoter upstream of the SIF-binding element

We previously reported that in transformed mouse sarcoma cells of spontaneous origin and in revertants transfected with a fos-cat fusion, the 600-bp c- fos promoter region provides chloramphenicol acetyltransferase activity. In the present study, we investigated the binding of transcriptional factor protein(s) to a region (−503 to −361) upstream of the sis (platelet-derived growth factor) -inducible factor (SIF) -binding element. Gel electrophoresis retardation (GER) assay clearly demonstrated the appearance of strong binding activity to a newly described fragment in the 142-bp region studied. Further analysis using synthetic oligodeoxyribonucleotides and GER defined a binding region of 30 bp ( AvaI- AvaII) from −503 to −472 that partially overlaps with a region known to bind fos promoter binding site 2 (FBS2). DNase I footprint analysis discovered a novel sequence in the upstream region of the c- fos promoter to which protein (s) in nuclear extracts from various mouse and human cells bind. This factor(s) is not identical to most known transcriptional factors present in the promoter region of nuclear oncogenes. A proximal part of this fragment is very conservative and contains several AP-2-like-binding sites.