Cbk1p and Hym1p are necessary for the daughter cell specific
localization of the transcription factor Ace2p.
Waldemar J. Racki (1), Anne-Marie Bécam (1), Edouard Bertrand (2),
Christopher J. Herbert (1)
(1) Centre Génétique Moléculaire, C.N.R.S., Ave de la Terrasse, Gif-sur-Yvette, 91190, France;
(2) Institute de Génétique Moléculaire de Montpellier, 34293 Montpellier
Cedex 5, France.
The protein kinase Cbk1p plays a crucial role in regulation of cellular
morphogenesis, deletion of the gene leads to a loss of polarity and the
formation of large aggregates of cells. This last phenotype is due to an
absence of activation of the transcription factor Ace2p, which is
necessary for the transcription of chitinase and other genes involved in
cell separation. The deletion of HYM1 leads to similar phenotypes
to the deletion of CBK1 except that hym1/hym1 diploids are
unable to sporulate. Ace2p is regulated at several levels, the gene is
specifically transcribed in G2 and significant quantities of the protein
are only found in the nucleus during M/G1. In wild type cells when Ace2p
is present in the nucleus it is specifically localized in the daughter
cell and not the mother cell nucleus. Deletion of either CBK1 or
HYM1 leads to a loss of this daughter/mother cell partition in
Ace2p nuclear localization. We have previously isolated extragenic
suppressors of the deletion of CBK1, dominant suppressors in
ACE2 and recessive suppressors in an unidentified gene. These
mutations also lead to a loss of the daughter cell specific localization
of Ace2p. We have used in situ hybridization to show that the
localization of Ace2p is not mRNA dependent and 'green RNA' to show that
Ace2p targets are daughter cell specific. These results show that Cbk1p,
Hym1p and other proteins are needed for both the daughter cell specific
localization and the activation of Ace2p.
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