Abstract: NIH3T3 cells' total RNA was extracted at various lengths of time after the cells were induced to re-enter the cell cycle from quesent stage by serum stimulation and at G₁,S,G₂ and M phases synchronized by double thymidine block and colcemid block.These samples were then analyzed by dot hybridization to determine the levels of c-fos and c-jun mRNA.Our results show that the peaks of c-fos and c-jun mRNA accumulation were found at 1 h after serum stimulation.Besides,it shows a second c-jun mRNA accumulation peak at 16h after serum stimulation.For the continuous growing cells,c-fos was found to be in low expression in every phases of cell cycle,whereas c-jun was found to have a high level of expression in S phase.These results suggest that in addition to the associated function of c-fos and c-jun in cells which are entering cell cycle,c-jun protein may play a unique role in G₁/S phase which does not need c-fos protein to cooperate with.

Key words: c-fos oncogene, c-jun oncogene, gene expression, cell cycle