Erythromycin and cycloheximide sensitivities of protein and RNA Synthesis in sporulating cells of Saccharomyces cerevisiae: Environmentally induced modifications controlled by chromosomal and mitochondrial genes.

The purpose of the experiments reported below was to examine the response in sporulation medium of the three diploid cell types MATα MATα, MATα MATα (asporogenic diploids) and MATα MATα (sporogenic diploid) to erythromycin, a specific inhibitor of mitochondrial protein synthesis (MPS) in vegetative cultures, and cycloheximide, a specific inhibitor of cytosol protein synthesis (CPS) in vegetative cultures. When MATα MATα diploids are transferred to sporulation medium a significant fraction of total protein synthesis (CPS + MPS) becomes sensitive to erythromycin in contrast to the behavior of MATa MATa and MATα MATα diploids in which the resistance of CPS to erythromycin is maintained. The decompartmentalization of erythromycin sensitivity is thus cell type specific. Erythromycin stimulates total RNA synthesis of MATα MATα cells in sporulation medium but not of MATα MATα and MATα MATα cells. Cycloheximide inhibits protein synthesis and stimulates RNA synthesis in all three diploid cell types. An erythromycin resistant mutant, shown to be due to a mutation of the mitochondrial genome, exhibited only partial resistance of CPS to erythromycin in sporulation medium in the background of the MATα MATα mating type genotype. Total RNA synthesis in this mutant was not stimulated. The results reported indicate that mitochondrial functions during sporulation are not restricted to those involving respiratory metabolism.