Effect of cell cycle position on thermotolerance in Saccharomyces cerevisiae

Abstract

We showed that the heat killing ,curve for exponentially growing Saccharomyces cerevisiae was biphasic. This suggests two populations of cells with different therpial killing characteristics. Whep exponentially growing cells separated into cell cycle-specific fractions via centrifugal elutriation were, heat shocked, the fractions enriched in smnall unbudded cells showed greater resistance to heat killing than did other cell cycle fractions. The lethal effects of extreme temperature on Saccharomyces cerevisiae have been described. Exponentially growing cells are much more sensitive than are stationary-phase cells to a thermal shock (15). Thus, resting or quiescent cells are more thermotolerant than growing cells are. This heat resistance is acquired as the cells pass from the exponentially growing to the stationary state (12). Schenberg-Frascino and Moustacchi (15) isolated small unbudded cells from stationary cultures and observed their thermotolerance as they progressed through the first cell cycle into exponential growth. They observed that thermotolerance is decreased in budding cells. Yeast cells, when starved for an essential nutrient such as nitrogen, phosphorous, or sulfur, cease dividing and arrest their cell division as unbudded cells. The thermotolerance of cells starved for any of these nutrients resembles that of stationary-phase cells, and it has been suggested that this thermotolerance is a general characteristic of resting cells (11).Our aim was to clarify the relationship between the cell cycle and thermotolerance. To this end we examined the effect of the cell cycle position on the thermotolerance of S. cerevisiae in exponentially growing cultures by using the elutriator rotor to separate cells by size and cell cycle position (9). We also examined the effects on the cell cycle of a mild heat shock, during which the cells acquire thermotolerance (10, 13). In addition, we used several methods to arrest cells in the unbudded state, and we determined the thermotolerance of the resulting populations. The methods included arrest via deprivation of essential nutrients, alphafactor arrest, and the use of temperature-sensitive cell division cycle mutants. Our results demonstrate that a distinct population of unbudded cells was more thermotolerant than were cells in other morphological stages in the cell cycle. We suggest that this thermotolerance is associated with a defined state, G0, which has synthetic and physiological properties distinct from those of other unbudded cells. MATERIALS AND METHODSStrains. The following strains were used: SKQ2n (a/a adell+ +/ade2 +Ihisl); A364A (a lys2 tyrl his7 gall adel ade2 ural); cdc7-1 (ts124); cdc25-1 (ts321); cdc33-1 (El7a), derived from A364A (4; provided by L. Hartwell); cdc35-1 (BR214-4a; a adel ural his7 arg4 trpl); and cdc36-12 (ST21; a met2 cyh2) (provided by L. Hartwell).Media and cell growth.

Global changes in protein synthesis during adaptation of the yeast Saccharomyces cerevisiae to 0.7 M NaCl

“…A cell cycle-dependent relation to cellular heat resistance has been proposed, and the majority of cells remain unbudded during the acquisition of thermotolerance (36). It was evident from the constant proportion of budding cells throughout the period of adaptation to salt that cells were frozen at their actual point in the cell cycle at the time of dehydration.…”

Constitutive Flocculation inSaccharomyces cerevisiae Through Overexpression of theGTS1 Gene, coding for a ‘Glo’-type Zn-finger-containing Protein

“…So, it might be that a culture of cells overexpressing GTS1 contains on average more cells in the G1 phase relative to a culture with control cells. Since cells in the G1 phase are more thermotolerant than cells in other cell cycle phases (Plesset et al, 1987), the former phenotypic effect of GTS1 overexpression might explain why the GTS1 could be cloned as described.…”

Delayed Correlation of mRNA and Protein Expression in Rapamycin-treated Cells and a Role for Ggc1 in Cellular Sensitivity to Rapamycin

“…Two replicate experiments were performed. One AD value was attributed to each dilution (1)(2)(3)(4)(5)(6), and the sum of the six AD product was used to compare growth fitness between each deletion strain and the wildtype strain (BY4741) with and without rapamycin. The growth fitness difference was measured by -fold change ratio as follows.…”

“…TOR is highly conserved from yeast to human and promotes cell growth in response to nutrient availability. Therefore, TOR inhibition through rapamycin treatment mimics a nutrient starvation phenotype induced by inhibition of protein synthesis (5), acquisition of thermotolerance (6), autophagy (7), and glycogen accumulation (5). Molecular mechanisms underlying protein synthesis inhibition by rapamycin involve inhibition of translation initiation (5,8) and ribosome biogenesis (9).…”