Figure 6.—

Silencing can be established in the absence of S-phase passage. Strain YSH241 was grown at 23° and blocked at G₂/M with nocodazole. After >90% of the cells in the culture exhibited a large bud morphology the culture was divided and subjected to the indicated temperature shifts. At the release point nocodazole was washed out of the media and the culture was resuspended in media containing α-factor. All cultures spent the same total amount of time in nocodazole. The table shows the percentage of cells with the morphologies listed following 5-hr incubation in α-factor. Shmoos are a subset of unbudded cells. Data shown are from one of three experiments that produced essentially identical results. For pedigree experiments the same protocol was followed, except that at the wash step cells were placed on solid YPD media containing α-factor. Released from the nocodazole-induced block, large-budded cells continued through the cell cycle and were either sensitive to α-factor, forming shmoos, or not sensitive, forming buds (cells that neither budded nor formed shmoos, always <10% of the total, were not counted). The final (“pedigree”) column indicates the percentage of large-budded cells in which at least one of the cell-cell pair exhibited sensitivity to α-factor by forming a shmoo. Data shown are the cumulative results of two independent experiments. At least 70 large-budded cells were assayed for each condition.