title: Degradation of cyclin B is required for the onset of anaphase in Mammalian cells.
abstract: Recently, it has been shown that cyclin B1 was degraded mainly before the onset of anaphase in mammalian cells. When a nondegradable form of cyclin B1 was introduced into cells, the metaphase-anaphase transition was blocked. This blockage was not due to a failure in activating anaphase-promoting complex, nor was it due to a failure of degradation of securin. To resolve the question of whether this blockage by overexpressing the nondegradable form of cyclin B1 is physiologically relevant or not, we developed a novel method to estimate the relative protein level of the overexpressed cyclin B1 mutant within an individual cell. We found that a low level of nondegradable cyclin B1 (less than 30% of the endogenous cyclin B1) was sufficient to block the metaphase-anaphase transition, implying that the blockage of anaphase onset by the nondegradable cyclin B1 was not due to an artifact of excessive M-phase-promoting factor activity. This result suggests that, in mammalian cells, the majority of cyclin B1 must be destroyed before the cell can enter anaphase.
authors.affiliation: Department of Biology, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China. bochang@ust.hk
authors.forename: Donald C
authors.initials: DC
authors.lastname: Chang
authors.forename: Naihan
authors.initials: N
authors.lastname: Xu
authors.forename: Kathy Q
authors.initials: KQ
authors.lastname: Luo
mesh_terms: D000705:Anaphase / Q000502:physiology*; D064173:Anaphase-Promoting Complex-Cyclosome; D019926:Cyclin B / Q000378:metabolism*; D056744:Cyclin B1; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D008164:Luminescent Proteins / Q000378:metabolism; D008677:Metaphase; D008938:Mitosis; D009363:Neoplasm Proteins / Q000378:metabolism; D064249:Securin; D013997:Time Factors; D043743:Ubiquitin-Protein Ligase Complexes / Q000502:physiology
chemical_list: C534699:CCNB1 protein, human; D019926:Cyclin B; D056744:Cyclin B1; D008164:Luminescent Proteins; D009363:Neoplasm Proteins; D064249:Securin; C578002:pituitary tumor-transforming protein 1, human; D049452:Green Fluorescent Proteins; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome