Zhelev N Z, Todorov I T, Philipova R N, Hadjiolov A A
Department of Molecular Genetics, Bulgarian Academy of Sciences, Sofia.
J Cell Sci. 1990 Jan;95 ( Pt 1):59-64. doi: 10.1242/jcs.95.1.59.
The preparation of mammalian cells for entry into mitosis is related to a cascade of G2 phase phosphorylations of several nuclear proteins driven by mitosis-specific protein kinases. Using a monoclonal antibody we have identified previously in mammalian cells a 125K/pI6.5 protein, associated with the nuclear matrix, and markedly increased in mitotic cells, which was named 'mitotin'. Here, we show by short-term [35S]methionine labeling of cell cycle synchronized cells that this protein is synthesized at comparable rates throughout interphase. However, upon cycloheximide block of protein synthesis mitotin labeled during S phase is rapidly degraded, while the degradation of mitotin labeled during late G2 phase is abolished, resulting in its net and marked increase. The accumulation of mitotin in premitotic and mitotic cells is related to its phosphorylation and the metabolic stability of its two phosphorylated forms. The metabolic stabilization and accumulation of a nuclear matrix protein upon phosphorylation suggests the operation of a novel mechanism among the complex events preparing the cell for mitosis.
哺乳动物细胞进入有丝分裂的准备过程与由有丝分裂特异性蛋白激酶驱动的几种核蛋白的G2期磷酸化级联反应有关。我们先前使用一种单克隆抗体在哺乳动物细胞中鉴定出一种与核基质相关的125K/pI6.5蛋白，在有丝分裂细胞中显著增加，该蛋白被命名为“有丝分裂素”。在这里，我们通过对细胞周期同步化的细胞进行短期[35S]甲硫氨酸标记表明，这种蛋白在整个间期以相当的速率合成。然而，在蛋白质合成被放线菌酮阻断后，S期标记的有丝分裂素迅速降解，而G2期后期标记的有丝分裂素的降解被消除，导致其净增加且显著增加。有丝分裂素在有丝分裂前期和有丝分裂细胞中的积累与其磷酸化以及两种磷酸化形式的代谢稳定性有关。一种核基质蛋白在磷酸化后代谢稳定并积累，这表明在细胞为有丝分裂做准备的复杂事件中存在一种新机制。
