Fig. 2. The G1 arrest of orp1-4 cells is checkpoint dependent. (A) Exponentially growing orp1-4 and the indicated orp1-4 checkpoint double mutant cells were shifted to the restrictive temperature of 36°C and cutting was monitored by DAPI staining. (B) orp1-4 rad9-HA and cdc17 rad9-HA cells were shifted to the restrictive temperature for the indicated times and the phosphorylation of Rad9-HA was monitored by SDS-PAGE and western blotting. (C) orp1-4, cdc18-K46 orp1-4 and orp1-4 rad26::ura4⁺ cells were synchronised by lactose gradient centrifugation in G2, and then shifted to the restrictive temperature. Septation index was determined by Calcofluor staining; cutting was measured by DAPI staining.