Yeast cells recover from mating pheromone alpha factor-induced division arrest by desensitization in the absence of alpha factor destruction.

S A Moore

doi:10.1016/s0021-9258(17)43557-5

Abstract

Saccharomyces cerevisiae MATa cells arrest cell division in response to the mating pheromone, alpha factor. After some interval of time the cells resume division. It is demonstrated here that cells recover from division arrest by becoming insensitive to the alpha factor under conditions of low cell density (10(2) cells/ml) where no alpha factor destruction occurs. The time of desensitization occurs later at higher alpha factor concentrations. Using the technique of perfusion photomicroscopy developed in this study, it was found that 95% of the desensitized cells remain insensitive to the alpha factor for greater than or equal to 3 generations at the alpha factor concentration where recovery occurred. Upon recovery, cells have generation times which are similar or identical to the calculated time from the cdc28 "start" step of cell division to cell separation. Therefore, the abnormally large recovered cells behave as if they have no growth time requirement for cell division for several generations. Desensitization was found to occur asymmetrically for parent and daughter cells. While parents (cells which have budded) are insensitive to alpha factor, their daughters (cells which have never budded and which were formed from desensitized parents during continuous perfusion with alpha factor) show 54% with a delayed generation time compared to control daughter cells.

Highlights

Bemost informative comparison of daughter cells in any case is cause desensitized cells in the R state remain insensitive for between those formed from parents which had recovered by several generations a t least, it can be concluded that the desensitizationin a factor and those formed from parents conversion of R back to A is slow and insignificant
Thedaughter cells are desensitized, buttheir desensitized parents are inhibited on the average by a factor from giving to them the necessary material to have the accelerated generation times seen for daughter cells formed upon a factor washout
Recovery by Desensitization Is Followed by a Shortened GenerationTime”381G cells which havebeen arrested for several hours by a factor and recovered by becoming insensitive have an average generation timewhich is accelerated compared to controlcells

Summary

EXPERIMENTAL PROCEDURES’

Materials-S.cerevisiae haploid strains usedwere381G MATa SUP4-3 cryl his580 trpl ade2-I tyrl lys (381G), and X2180-1A MATa [20]. The kinetics of bud emergence upon CY factor washout for cells embedded in agar were obtained after perfusing the gel with medium containing 3.3 nM a factor for 6 h. The cells were immediately sonicated and embedded in a 1%noble agar sandwich which was perfused with medium lacking a factor for the photomicroscopy. Cells in a 1%noble agar sandwich were perfused with medium plus 1nM a factor for 5 h, thenperfused with medium lacking a factor during which photomicroscopy was done These two methods gave average P and D generation times whichwere identical within 5 and 15%, respectively, and the data were pooledfor Table I1 (see "Results"). S the a factor fraction remaining in the agar slab during steady state perfusion This equation describes the first order destruction of CY factor by the cell-associatedprotease [18]during the time period, t8.*d,uring which kt,. Desensitization of Yeast Cells to a Factor ably assumed that themedium is replaced around and within colonies at thesame rate

RESULTS

DISCUSSION

Constant perfusion at