The objective of this experiment is to identify the S. cerevisiae genes that provide a selective advantage or disadvantage for cell survival in the space environment. The genes which convey a survival advantage and those that determine a survival disadvantage in response to spaceflight will be identified by whole genome microarray-mediated fitness expression profiling of diploid homozygous and heterozygous S. cerevisiae cultures. The results will be compared to those obtained when the same experiments are performed, with the identical microbes cultured under ground-based conditions of modeled microgravity.
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The experiment involves use of a mixture of molecularly engineered isogenic yeast strains that differ only in a single gene locus. Each gene has been replaced with an identifying "bar code" and the mixture contains a deletion strain for every gene in the yeast genome. The yeast deletion strain mixture will be dried down and spotted on filter paper pre-flight which will grant the experiment flexibility in terms of on-orbit activation time. Experiment activation on orbit will commence with introduction of YPD (Yeast extract, peptone, dextrose) media. The cultures will be allowed to grow at ambient temperature under the selective pressure of microgravity. After a growth period of 60-72 hours the experiment will be terminated by introduction of the fixative RNALater II. The experiment will be maintained at ambient temperature until return from flight. Upon return from flight the cultures will be returned to the PI/Co-I's laboratory. The Deoxyribonucleic Acid (DNA) will be extracted, and the bar codes amplified by Polymerase Chain Reaction (PCR). The resulting product will be annealed to a gene microarray chip comprising spots for the complementary sequence of each barcode. In this manner the selective growth of every strain in the yeast deletion series can be assayed in a single tube, enabling a genomic approach to phenotypic analyses. This study will identify the genes, which provide a selective advantage or disadvantage for cell survival in space.
Due to Hurricane Katrina post flight processing and DNA analysis of samples are on hold.
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