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A more recent version of this article appeared on December 1, 2004
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Submitted on March 25, 2004
Revised on September 2, 2004
Accepted on September 7, 2004
*Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720;
Howard Hughes Medical Institute and Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143
Monitoring Editor: Trisha Davis
The regulation and timing of spindle pole body (SPB) duplication and maturation in fission yeast was examined by TEM. When cells are arrested at G1 by nitrogen starvation, the SPB is unduplicated. On release from G1, the SPBs were duplicated after 1-2 h. In cells arrested at S by hydroxyurea, SPBs are duplicated but not mature. In G1 arrest/release experiments with cdc2.33 cells at the restrictive temperature, SPBs remained single, while in cells at the permissive temperature, SPBs were duplicated. In cdc10 mutant cells, the SPBs appear not only to be duplicated but also undergo partial maturation including invagination of the nuclear envelope underneath the SPB. There may be an S-phase specific inhibitor of SPB maturation whose expression is under control of cdc10+. This model was examined by induction of overreplication of the genome by overexpression of rum1p or cdc18p. In cdc18p overexpressing cells, the SPBs are duplicated but not mature suggesting that cdc18p is one component of this feedback mechanism. In contrast, cells overexpressing rum1p have large, deformed SPBs accompanied by other features of maturation and duplication. We propose a feedback mechanism for maturation of the SPB that is coupled with exit from S to trigger morphological changes.
Corresponding author.
E-mail: Zcande{at}uclink4.Berkeley.edu