The Hsp40 Molecular Chaperone Ydj1p, Along With the Protein Kinase C Pathway, Affects Cell-Wall Integrity in the Yeast Saccharomyces cerevisiae

摘要

Molecular chaperones, such as Hsp40, regulate cellular processes by aiding in the folding, localization,nand activation of multi-protein machines. To identify new targets of chaperone action, we performed anmulti-copy suppressor screen for genes that improved the slow-growth defect of yeast lacking the YDJ1nchromosomal locus and expressing a defective Hsp40 chimera. Among the genes identified were MID2,nwhich regulates cell-wall integrity, and PKC1, which encodes protein kinase C and is linked to cell-wallnbiogenesis. We found that ydj1D yeast exhibit phenotypes consistent with cell-wall defects and that thesenphenotypes were improved by Mid2p or Pkc1p overexpression or by overexpression of activated downstreamncomponents in the PKC pathway. Yeast containing a thermosensitive allele in the gene encodingnHsp90 also exhibited cell-wall defects, and Mid2p or Pkc1p overexpression improved the growth of thesencells at elevated temperatures. To determine the physiological basis for suppression of the ydj1D growthndefect, wild-type and ydj1D yeast were examined by electron microscopy and we found that Mid2pnoverexpression thickened the mutant’s cell wall. Together, these data provide the first direct link betweenncytoplasmic chaperone function and cell-wall integrity and suggest that chaperones orchestrate the complexnbiogenesis of this structure.