Actin Protein And Chromosomal Build Relations Within The Nucleus

Actin is an important protein in cytoplasm, playing numerous cytoplasmic roles. Recently, A great number of biochemical analyses and immunoctochemical experiments have proved that actin presents in nuclei and chromosomes in plants and animals, showing that actin is involved in the nuclear processes such as chromosome condensation, RNA transcription and so on. In order to avoid the possible contamination of the cytosolic actin, we ultilized a cell-free system to study the effect of nuclear actin on the process of chromosome construction.In this paper, the effect of nuclear actin on the process of chromosome construction has been studied by utilizing the precise natural synchrous plasmodium of Physarum polycephalum, SDS-polyacryl amide gel electrophoresis (SDS-PAGE), western blotting, the cell-free system and optics microscopy. The major results and conclusions are as follows:1. A synchronous mitotic experiment system that was in an unchanged culture condition was established. SDS-PAGE and western blotting of plasmodia of Physarum polycephalum showed that cyclin B was present in the plasmodia of S phase, G2 phase, prophase, and metaphase. The molecular weight of Cyclin B in Physarum polycephalum was around 62kDa. Cyclin B was gradually accumulated from S phase to metaphase, and reached the maximal level at metaphase, however disappeared in the plasmodia of anaphase and telophase. Cyclin B can be a kind of mark protein which represents the process of prophase.2. Mitotic extracts were prepared from the synchronous metaphase plasmodia of Physarum polycephalum. The results of western blotting indicated that cyclin B was a component of the mitotic extracts of Physarum polycephalum. After the nuclei of late G2 phase were incubated in the mitotic extracts harvested from metaphase plasmodia, the cyclin B in the nuclei gradually accumulated with the prolongation of incubating time. While, in the control group, the content of cyclin B changed little. This indicated that the mitotic extracts of metaphase plasmodia had the activity of accelerating the process of prophase, and the cell free system with MPF activity was established.3. The nuclei of the late G2 phase treated by cytochalasinB were incubated in the mitotic extracts harvested from the metaphase plasmodia. Western blotting analysis showed that the content of cyclin B in the nuclei changed little. In contrast, in the control group, the content of cyclin B gradually increased with the prolongation of incubating time. Our results showed that the treatment of cytochalasin B affected the increase of the cyclin B content in the nuclei directly. As cyclin B is the mark protein representing the process of prophase, we infered that cytochalasin B destroyed the polymerization of the nuclear actin and directly affected the process of prophase. Nuclear actin played an important role in the process of the chromosome construction.