Preparation and Partial Characterization of Old Yeast Cells

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Abstract
Age-synchronized populations of the budding yeast Saccharomyces cerevisiae were prepared by a combination of growth-synchronization methods and cell separation by rate-zonal sedimentation in density gradients. The procedure allowed the bulk preparation of cells of any desired age up to at least 20 generations with minimum yields of 108 cells per preparation, starting with 6 × 109 0-generation cells. The purity of the preparations was >90%, with an accuracy of ±2 generations. The procedure itself had no detrimental effects on the cells, as indicated by a number of physiological parameters. Cell viability and resistance to sonication remained essentially unchanged during aging. In contrast, cell size and generation time increased, providing biomarkers for the aging process. The procedure described here should help establish yeast as a useful model system for studies of cellular aging at the molecular level.