Background：c-FOS, also named as Proto-oncogene c-Fos and G0/G1 switch regulatory protein 7, is a 380 amino acid protein, which contains 1 bZIP(basic-leucine zipper) domain and belongs to the bZIP family. FOS is expressed at very low levels in quiescent cells. When cells are stimulated to reenter growth, FOS undergo 2 waves of expression, the first one peaks 7.5 minutes following FBS induction. At this stage, the FOS protein is localized endoplasmic reticulum. The second wave of expression occurs at about 20 minutes after induction and peaks at 1 hour. At this stage, the FOS protein becomes nuclear. The calculated molecular weight of FOS is 40 kDa, but Phosphorylated FOS protein is about 60-65 kDa.
