ABSTRACT
Using an anti-nucleolar protein B23 monoclonal antiboby, we examined the changes of protein B23 content in NIH3T3 fibroblasts during serum-induced proliferation and the difference in protein B23 content between mitotic and interphase NIH3T3 fibroblasts by immunofluorescence and im-munoblot methods. When NIH3T3 cells grew confluent, the serum containing medium was removed and replaced by serum-free medium,and the cells were cultured for another 24h. Then cells were refed with serum and further cultured. The results showed that protein B23 content was low in serum-starved NIH3T3 cells,and it markedly increased after serum addition. Furthermore,the increase occurred early at 6h after serum treatment. It was also showed that protein B23 content in mitotic cells blocked by the microtubule inhibitor colcemid was much higher than that in interphase ones. Our results suggested that nucleolar protein B23 might play some roles in the early stage of serum- induced proliferation and during transition from G2 to mitosis in cell cycle.