Yeast fungi

Aging is a process characterized by accumulated oxidative damage to DNA, proteins, and lipids,which leads to the gradual degeneration of cellular activity. Mitochondria play a central role in aging because they produce both cellular energy and oxidative stress. As resultof accumulated oxidative damage, mitochondria function decays, which leads to a cellular energy deficit and compromises cellular function. Iron is an essential nutrient reequired by mitodhondria to function optimally. It has been proved that iron supplementation increases the lifespan of several yeast strains, including superoxide dismutase mutants. We are interested in finding where the iron is going and what it might be doing that is beneficial to the cell. We have used Saccharomyces cerevisiae as our molecular model of aging. Our results indicate that the extra iron is being transported into the mitochoindria.

Aconitase is an important enzyme in the citric Acid Cycle, is needed for maintenance of mitochondrial DNA, is a key regulator of iron in the cell, and is very sensitive to oxidative stress. We have isolatd the yeast ACO1 gene, which codes for aconitase, and randomly mutated it to create a mutant library of cells each expressing a different version of ACO1. We will select for oxidative stress resistant aconitase in S. cerevisiae by subjecting strains to successive rounds of heat shock and competitive growth against other mutants. The "winner" of this competition will then be analyzed for which version of aconitase it is expressing, which may lead to increased longevity.

In my thesis work, I attempted to construct a plasmid that would allow stable integration of genes into the Saccharomyces cerevisiae yeast genome under the control of the repressible TetO promoter. The yeast ACO1 gene was cloned under the control of the TetO operator and the tTA transactivator. This construct was inserted into yeast cells in order to observe the effects of aconitase overexpression on aging. Unfortunately, the transformed cells appeared incapable of aconitase expression as determined by glutamic acid auxptrophy, a phenotype of aconitase mutants. We have sequenced the pIT1ACO1 plasmid and have found many abnormalities in the promoter region. If the plasmid can be made to function as intended, the resulting yeast strain can be used in the future to determine if aconitase plays an important role in cellular aging.