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The Cell Cycle of the Budding Yeast Sterigmatomyces halophilus: Levels of Mitochondrial Components in Mother and Bud Cells
Abstract
Sterigmatomyces halophilus is an unusual budding yeast in which daughter cells are formed remote from the mother cell on fragile projections called sterigmata. These sterigmata are readily disrupted by ultrasonication, allowing easy detachment of immature buds from their mother cells. Fractions containing cells at different stages of the cell cycle, obtained by isopycnic fractionation of exponentially growing cultures, were treated ultrasonically to produce a mixture of immature buds, mothers and mother-bud doublets. Rate-sedimentation of these suspensions using sucrose gradients produced three discrete bands corresponding to each of these populations. The activities of succinate dehydrogenase and cytochrome c oxidase were measured in extracts prepared from (1) the cells recovered from the slowest sedimenting band (i.e. immature buds) and (2) the original population (i.e. mother-bud doublets). The activity of each enzyme, expressed on a per cell basis, varied in phase with the observed activity in the mother-bud doublets during the cell cycle, and when expressed as specific activity was the same in both daughter and mother-daughter pairs. This indicates that these two enzymes (and by implication inner mitochondrial membrane) are evenly distributed between mother and developing daughter cells during the cell cycle.
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© Society for General Microbiology, 1983