The Mob2p-Cbk1p kinase complex promotes polarized growth and acts
with the Mitotic Exit Network and nuclear export regulation to
facilitate asymmetric transcription factor localization in S.
cerevisiae .
Cornelia Kurischko (1), Eric Weiss (2),
David Drubin (2), Frank Luca (1)
(1) Dept. of Animal Biology,
University of Pennsylvania, 3800 Spruce Street, Philadelphia, PA 19104,
USA; (2) Dept. of Molecular and Cellular Biology, University of
California, Berkeley
Accurate spatial and temporal control of
processes that determine cell morphology is important for productive
cell growth and division. Budding yeast cells lacking the Ndr/LATS-related protein kinase Cbk1p fail to sustain polarized growth during
early bud morphogenesis and mating projection formation. Cbk1p is also
required for Ace2p-dependent transcription of genes involved in
mother/daughter separation following cytokinesis. Here we show that the
conserved protein Mob2p is required for Cbk1p function. Mob2p and Cbk1p
physically associate and interdependently localize to incipient bud
sites and the daughter cell cortex during bud emergence and growth.
Mob2p is required for both full Cbk1p kinase activity and Cbk1p
hyperphosphorylation in vivo. At the end of mitosis, Mob2p and
Cbk1p localize to the bud neck and daughter cell nuclei. Restriction of
Ace2p to daughter cell nuclei requires Mob2p, Cbk1p, and a functional
nuclear export pathway. Nuclear localization of Mob2p and Ace2p does not
occur in mob1-77 mutants, which are defective in Mitotic Exit
Network (MEN) signaling, even when mob1-77 cell cycle arrest is
bypassed. Collectively, these data indicate that Mob2p-Cbk1p has three
functions: 1) to maintain polarized cell growth; 2) to prevent the
nuclear export of Ace2p from the daughter cell nucleus following mitotic
exit and 3) to coordinate Ace2p-dependent cell separation with MEN
activation.
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