A common SSD1 truncation is toxic to cells entering quiescence and promotes sporulation

Abstract

Ssd1p is an RNA binding protein in Saccharomyces cerevisiae that plays an important role in cell division, cell fate decisions, stress response and virulence. Lab strain W303 encodes the terminal truncation ssd1-2, which is typically interpreted to be a loss of function allele. We have shown that ssd1-2 is toxic to mpt5-Δ mutants and to diploids entering stationary phase and quiescence. The ssd1-Δ null shows no toxicity, indicating that ssd1-2 is disrupting an essential function that does not solely require Ssd1p. ssd1-2 cells are also more sensitive to stress than ssd1-Δ . These phenotypes are recessive to SSD1-1 . In contrast, ssd1-2 plays a dominant role in promoting sporulation.

Figure 1. The ssd1-2 truncation found in W303 is toxic to cells entering quiescence but promotes sporulation.

The genotypes used in each plot are indicated in the legend and the number of replicates is listed above, in legend order. (A and B) Percent of viable cells as a function of days after inoculation into rich glucose medium. (C) Innate tolerance to growth on plates containing the detergent Sodium Dodecyl Sulfate (SDS). (D) Acquired stress tolerance induced by treating cells for 30 minutes at 37° C, then shifting to 53° C for 30 minutes before making serial dilutions and plating. (E) Increased sensitivity of ssd1-2 to SDS is recessive. Innate tolerance to SDS in diploids, genotypes indicated on the left. (F) Quiescence defect of ssd1-2 is recessive. Percent of dense quiescent cells purified from seven day cultures. (G) Sporulation promoted by ssd1-2 is dominant. Percent of spore-containing asci induced by limiting cells for nitrogen and glucose.