The Role Of Superoxide Dismutases In Yeast Thermo Tolerance

Since the heat shock proteins have been discovered, understanding how cells defend against heat stress has received substantial research interests. Howere, the molecular mechanism underlying cellular thermo tolerance has not been fully determined. Our laboratory has recently discovered that the well known anti-oxidant enzyme Cu,ZnSODl is essential for model organism yeast acquisition of thermo tolerance; deletion mutants of the genes encoding Cu,ZnSODl were unable to grow at non-permissive temperatures of 39℃. Using the yeast system, the current thesis research explored whether or not other known superoxide dismutases are able to confer thermo tolerance.We expressed Fe-SOD gene from E. coli or Mn-SOD gene from hyperthermophilic crenarchaeon Pyrobaculum aerophilum in a yeast mutant lacking its chromosomal SOD1 gene and tested whether or not the cells were able to grow at non-permissive temperatures of 39℃. Our results show that FeSOD and MnSOD both were able to rescue the growth of the sod1Δmutant at non-permissive temperatures of 39℃. The data therefore suggest that thermo tolerance is likely a general physiological function of superoxide dismutases.We also investigated whether or not CUP1 gene plays a role in thermo tolerance acquisition of yeast. Others have reported that when overexpressed, CUP1 was able to partly substitute SOD1 in defense against oxidative stress and that Cupl likely contains weak dismutase activity. We found that overexpression of CUP1 was unable to rescue the growth of the sod1Δmutant at non-permissive temperatures of 39℃. The data indicate that CUP1 is not required for yeast thermo tolerance.