Asc1 supports cell-wall integrity near bud sites by a Pkc1 independent mechanism.
BACKGROUND
The yeast ribosomal protein Asc1 is a WD-protein family member. Its mammalian ortholog, RACK1 was initially discovered as a receptor for activated protein C kinase (PKC) that functions to maintain the active conformation of PKC and to support its movement to target sites. In the budding yeast though, a connection between Asc1p and the PKC signaling pathway has never been reported.


RESULTS
In the present study we found that asc1-deletion mutant (asc1Delta) presents some of the hallmarks of PKC signaling mutants. These include an increased sensitivity to staurosporine, a specific Pkc1p inhibitor, and susceptibility to cell-wall perturbing treatments such as hypotonic- and heat shock conditions and zymolase treatment. Microscopic analysis of asc1Delta cells revealed cell-wall invaginations near bud sites after exposure to hypotonic conditions, and the dynamic of cells' survival after this stress further supports the involvement of Asc1p in maintaining the cell-wall integrity during the mid-to late stages of bud formation. Genetic interactions between asc1 and pkc1 reveal synergistic sensitivities of a double-knock out mutant (asc1Delta/pkc1Delta) to cell-wall stress conditions, and high basal level of PKC signaling in asc1Delta. Furthermore, Asc1p has no effect on the cellular distribution or redistribution of Pkc1p at optimal or at cell-wall stress conditions.


CONCLUSIONS
Taken together, our data support the idea that unlike its mammalian orthologs, Asc1p acts remotely from Pkc1p, to regulate the integrity of the cell-wall. We speculate that its role is exerted through translation regulation of bud-site related mRNAs during cells' growth.
Melamed
Daniel
D
Department of Biology, Technion-Israel Institute of Technology, Haifa, Israel.
Bar-Ziv
Lavi
L
Truzman
Yossi
Y
Arava
Yoav
Y
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000502:physiology*; D015153:Blotting, Western; D019204:GTP-Binding Proteins / Q000235:genetics / Q000502:physiology*; D011493:Protein Kinase C / Q000235:genetics / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000254:growth & development / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction
C111825:ASC1 protein, S cerevisiae; D048868:Adaptor Proteins, Signal Transducing; D029701:Saccharomyces cerevisiae Proteins; C490702:PKC1 protein, S cerevisiae; D011493:Protein Kinase C; D019204:GTP-Binding Proteins