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Mol. Cell. Biol., Feb 1997, 620-626, Vol 17, No. 2
Y Wang and DJ Burke
Saccharomyces cerevisiae, like most eucaryotic cells, can prevent the onset
of anaphase until chromosomes are properly aligned on the mitotic spindle.
We determined that Cdc55p (regulatory B subunit of protein phosphatase 2A
[PP2A]) is required for the kinetochore/spindle checkpoint regulatory
pathway in yeast. ctf13 cdc55 double mutants could not maintain a
ctf13-induced mitotic delay, as determined by antitubulin staining and
levels of histone H1 kinase activity. In addition, cdc55::LEU2 mutants and
tpd3::LEU2 mutants (regulatory A subunit of PP2A) were nocodazole sensitive
and exhibited the phenotypes of previously identified kinetochore/spindle
checkpoint mutants. Inactivating CDC55 did not simply bypass the arrest
that results from inhibiting ubiquitin-dependent proteolysis because
cdc16-1 cdc55::LEU2 and cdc23-1 cdc55::LEU2 double mutants arrested
normally at elevated temperatures. CDC55 is specific for the
kinetochore/spindle checkpoint because cdc55 mutants showed normal
sensitivity to gamma radiation and hydroxyurea. The conditional lethality
and the abnormal cellular morphogenesis of cdc55::LEU2 were suppressed by
cdc28F19, suggesting that the cdc55 phenotypes are dependent on the
phosphorylation state of Cdc28p. In contrast, the nocodazole sensitivity of
cdc55::LEU2 was not suppressed by cdc28F19. Therefore, the mitotic
checkpoint activity of CDC55 (and TPD3) is independent of regulated
phosphorylation of Cdc28p. Finally, cdc55::LEU2 suppresses the temperature
sensitivity of cdc20-1, suggesting additional roles for CDC55 in mitosis.
Copyright © 1997, American Society for Microbiology
Cdc55p, the B-type regulatory subunit of protein phosphatase 2A, has multiple functions in mitosis and is required for the kinetochore/spindle checkpoint in Saccharomyces cerevisiae
Department of Biology, University of Virginia, Charlottesville 22903, USA.
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