Phosphorylation state defines discrete roles for monopolin in chromosome attachment and spindle elongation.
Department of Molecular Genetics and Microbiology
Medical Subject Headings
Anaphase; Animals; CDC2 Protein Kinase; Cell Cycle Proteins; Chromosome Segregation; Chromosomes; Kinetochores; Metaphase; Mitotic Spindle Apparatus; Multiprotein Complexes; Phosphorylation; Protein Tyrosine Phosphatases; Recombinant Fusion Proteins; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Schizosaccharomyces; Schizosaccharomyces pombe Proteins; Transcription Factors
Microbiology | Molecular genetics
BACKGROUND: It is unknown how oscillations in Cdk1 activity drive the dramatic changes in chromosome and spindle dynamics that occur at the metaphase/anaphase transition.
RESULTS: We show that the Schizosaccharomyces pombe monopolin complex has distinct functions in metaphase and anaphase that are determined by the phosphorylation state of its Mde4 subunit. When Cdk1 activity is high in metaphase, Mde4 is hyperphosphorylated on Cdk1 phosphorylation sites and localizes to kinetochores. A nonphosphorylatable mutant of Mde4 does not localize to kinetochores, appears prematurely on the metaphase spindle, and interferes with spindle dynamics and chromosome segregation, illustrating the importance of Cdk1 phosphorylation in regulating metaphase monopolin activity. When Cdk1 activity drops in anaphase, dephosphorylation of Mde4 triggers monopolin localization to the mitotic spindle, where it promotes spindle elongation and integrity, coupling the late mitotic loss of Cdk1 activity to anaphase spindle dynamics.
CONCLUSIONS: Together, these findings illustrate how the sequential phosphorylation and dephosphorylation of monopolin helps ensure the orderly execution of discrete steps in mitosis.
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Citation: Curr Biol. 2009 Jun 23;19(12):985-95. Epub 2009 Jun 11.