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

Molecular chaperones, such as Hsp40, regulate cellular processes by aiding in the folding, localization, and activation of multi-protein machines. To identify new targets of chaperone action we performed a multi-copy suppressor screen for genes that improved the slow growth defect of yeast lacking the YDJ1 chromosomal locus and expressing a defective Hsp40 chimera. Among the genes identified were MID2, which regulates cell wall integrity, and PKC1, which encodes protein kinase C and is linked to cell wall biogenesis. We found that ydj1 yeast exhibit phenotypes consistent with cell wall defects and these phenotypes were improved by Mid2p or Pkc1p over-expression or by over-expression of activated down-stream components in the PKC pathway. Yeast containing a thermosensitive allele in the gene encoding Hsp90 also exhibited cell wall defects, and Mid2p or Pkc1p over-expression improved the growth of these cells at elevated temperatures. To determine the physiological basis for suppression of the ydj1 growth defect, wild type and ydj1 yeast were examined by electron microscopy and we found that Mid2p over-expression thickened the mutant's cell wall. Together, these data provide the first direct link between cytoplasmic chaperone function and cell wall integrity, and suggest that chaperones orchestrate the complex biogenesis of this structure.

Key Words: Hsp70, Hsp90, MID2, PKC1, SV40 T Antigen

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				C. N. Martineau, J.-M. Beckerich, and M. Kabani Flo11p-Independent Control of "Mat" Formation by Hsp70 Molecular Chaperones and Nucleotide Exchange Factors in Yeast Genetics, November 1, 2007; 177(3): 1679 - 1689. [Abstract] [Full Text] [PDF]

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