Summer 2007 REU Project
Regulation of copper homeostasis in Saccharomyces cerevisiae
Because copper is required for normal cellular growth, but is also toxic at high concentrations, all cells possess mechanisms to maintain physiological levels of copper. Cup1, a copper metallothionein, plays an essential role in this regulation. Cells rapidly activate the CUP1 gene upon exposure to toxic levels of copper. Cup1 sequesters excess intracellular copper, minimizing the harmful effect of the metal ion. However, complete removal of copper is prevented by rapid shutdown of the gene, the mechanism of which is currently being investigated in our lab. Mutants which fail to shutdown CUP1 have been previously identified in our lab. We tested the hypothesis that these mutants counteract their inability to shutdown CUP1 by inducing genes involved in copper uptake. Proteins expressed during copper starvation include Ctr1, a copper transporter which imports Cu(I), and Fre1, a reductase which reduces extracellular Cu(II) to Cu(I) for uptake by Ctr1. We measured the expression of CUP1, CTR1, and FRE1 mRNA in mutants exposed to excess copper using real time RT-PCR analysis. Surprisingly, we found that the mutants do not continue to overexpress CUP1 during long exposures to copper, and subsequently do not induce expression of CTR1 and FRE1. This suggests that mutant strains adapt to their initial misregulation of CUP1.
|
