The eukaryote chaperonin CCT is a cold shock protein in Saccharomyces cerevisiae

The eukaryotic Hsp60 cytoplasmic chaperonin CCT (chaperonin containing the T-complex polypeptide-1) is essential for growth in budding yeast, and mutations in individual CCT subunits have been shown to affect assembly of tubulin and actin. The present research focused mainly on the expression of the CCT subunits, CCTalpha and CCTbeta, in yeast (Saccharomyces cerevisiae). Previous studies showed that, unlike most other chaperones, CCT in yeast does not undergo induction following heat shock. In this study, messenger ribonucleic acid (mRNA) and protein levels of CCT subunits following exposure to low temperatures, were examined. The Northern blot analysis indicated a 3- to 4-fold increase in mRNA levels of CCTalpha and CCTbeta genes after cold shock at 4 degrees C. Interestingly, Western blot analysis showed that cold shock induces an increase in the CCTalpha protein, which is expressed at 10 degrees C, but not at 4 degrees C. Transfer of 4 degrees C cold-shocked cells to 10 degrees C induced a 5-fold increase in the CCTalpha protein level. By means of fluorescent immunostaining and confocal microscopy, we found CCTalpha to be localized in the cortex and the cell cytoplasm of S. cerevisiae. Localization of CCTalpha was not affected at low temperatures. Co-localization of CCT and filaments of actin and tubulin was not observed by microscopy. The induction pattern of the CCTalpha protein suggests that expression of the chaperonin may be primarily important during the recovery from low temperatures and the transition to growth at higher temperatures, as found for other Hsps during the recovery phase from heat shock.