Figure 2.—

Establishment of silencing at HML and HMR upon induction of Sir3. (A) Establishment of silencing is not observed at HMR at G1. YSH801 was grown to log phase in YPraffinose media. Half of this culture was blocked in G1 phase by addition of α-factor. Galactose was then added to one-half of the α-factor arrested cells. As a control, galactose was also added to the unblocked cycling cells. RNA was isolated at the indicated time points and levels of a1 and ACT1 were measured by RT–PCR. (B) Moderate silencing at HMR is observed in G2/M blocked cells. Strain YSH811 was grown to log phase in raffinose-containing media and subject to the same experimental design as described in A, except that nocodazole was used to block cells at G2/M. (C) Establishment of silencing is observed at HML at G2/M. α1 message was measured in the same cell cultures described in B.