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 spon taneous origin and in revertants transfected with a fos-cat fusion, th e 600-bp c-fos promoter region provides chloramphenicol acetyltransfer ase activity. In the present study, we investigated the binding of tra nscriptional factor protein(s) to a region (- 503 to -361) upstream of the sis (platelet-derived growth factor)-inducible factor (SIF)-bindi ng element. Gel electrophoresis retardation (GER) assay clearly demons trated the appearance of strong binding activity to a newly described fragment in the 142-bp region studied. Further analysis using syntheti c 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 an alysis discovered a novel sequence in the upstream region of the c-Sos promoter to which protein(s) in nuclear extracts from various mouse a nd human cells bind. This factor(s) is not identical to most known tra nscriptional factors present in the promoter region of nuclear oncogen es. A proximal part of this fragment is very conservative and contains several AP-2-like-binding sites.