Mutations in a small region of the exportin Crm1p disrupt the daughter cell-specific nuclear localization of the transcription factor Ace2p in Saccharomyces cerevisiae.
BACKGROUND
The CBK1 gene of Saccharomyces cerevisiae encodes a protein kinase that is a member of the NDR (nuclear Dbf2-related) family of protein kinases, which are involved in morphogenesis and cell proliferation. Previous studies have shown that deletion of CBK1 leads to a loss of polarity and the formation of large aggregates of cells. This aggregation phenotype is due to the loss of the daughter cell-specific accumulation of the transcription factor Ace2p, which is responsible for the transcription of genes whose products are necessary for the final separation of the mother and the daughter at the end of cell division.


RESULTS
We show that the daughter cell-specific localization of Ace2p does not occur via a specific localization of the ACE2 mRNA and that, in vivo, the transcription of CTS1, one of the principal targets of Ace2p, is daughter cell-specific. We have shown that extragenic suppressors of the Deltacbk1 aggregation phenotype are located in the nuclear exportin CRM1 and ACE2. These mutations disrupt the interaction of Ace2p and Crm1p, thus impairing Ace2p export and resulting in the accumulation of the protein in both mother and daughter cell nuclei.


CONCLUSIONS
We propose that in the daughter cell nucleus Cbk1p phosphorylates the Ace2p nuclear export signal, and that this phosphorylation blocks the export of Ace2p via Crm1p, thus promoting the daughter cell-specific nuclear accumulation of Ace2p.
Bourens
Myriam
M
Centre de Génétique Moléculaire du CNRS, UPR 2167, Gif-sur-Yvette F-91198, France.
Racki
Waldemar
W
Bécam
Anne-Marie
AM
Panozzo
Cristina
C
Boulon
Séverine
S
Bertrand
Edouard
E
Herbert
Christopher J
CJ
D021581:Active Transport, Cell Nucleus; D002455:Cell Division; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D002688:Chitinases / Q000235:genetics; D004268:DNA-Binding Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D005656:Fungal Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D028884:Karyopherins / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D017346:Protein Serine-Threonine Kinases; D021381:Protein Transport; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics* / Q000378:metabolism; D012097:Repressor Proteins / Q000032:analysis / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D013045:Species Specificity; D014157:Transcription Factors / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D000097606:Exportin 1 Protein
D002688:Chitinases; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D047908:Intracellular Signaling Peptides and Proteins; D028884:Karyopherins; D017346:Protein Serine-Threonine Kinases; D018160:Receptors, Cytoplasmic and Nuclear; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D000097606:Exportin 1 Protein; C066778:ACE2 protein, S cerevisiae; C098733:ASH1 protein, S cerevisiae; C423362:CBK1 protein, S cerevisiae; C121990:CTS1 protein, S cerevisiae