Significant and Systematic Expression Differentiation in Long-Lived Yeast Strains

The three yeast mutants sch9Δ, ras2Δ, tor1Δ show extended chronological life span up to three folds. This study aims to dissect the mechanisms that lead to the yeast life span extension. Keywords: Expression comparison between wild type and long-lived yeast mutant strain We obtain gene expression profiles of sch9Mutant, ras2Mutant, tor1Mutant as well as that for a wild type at day 2.5 in SDC medium using Affymetrix Yeast2.0 arrays. Each sample has three replicates. We use a complicated pre-processing method and get the expression differntiation directly. We consider the issue of processing robustness and expression large differentiation. The normalization is carried out in a pairwise fashion. Namely, for each wild type sample (W1, W2, W3), three replicates of a mutant are normalized with respect to each reference. Take sch9Mutant (triplicates: S1, S2 and S3) for example, the normalized arrays with respect to W1, W2, W3 are respectively denoted by S1\W1, S2\W1, S3\W1, S1\W2, S2\W2, S3\W2, S1\W3, S2\W3, S3\W3. We group the wild type and normalized mutant arrays by the reference, and then summarize each group. We summarize the four arrays (the reference plus three normalized) W1, S1\W1, S2\W1, S3\W1 together. This leads to three estimates of expression fold changes of the mutant versus the wild type. In total, we have nine estimates from three wild type references, and we take their median difference as the final estimate. Expression fold change estimates (generated by the analysis) are given in the Series table.