FIG. 4.

Mus81 is important for survival under conditions that stall replication forks. (A) mus81 cells are sensitive to HU. Serial 10-fold dilutions (10⁴ to 10¹) of cells were incubated on agar medium supplemented with no HU or 5 mM HU. (B) Cds1 is activated normally by HU treatment in mus81 cells. Wild-type (WT), mus81, and cds1 strains were incubated in the presence (+) or absence (−) of HU for 3 h. Cds1 activity was measured with the GST:Wee1¹⁵² substrate as previously described (6). SDS, sodium dodecyl sulfate. (C) The mus81 mutation lowers the restrictive temperature of thermosensitive DNA polymerase delta (polδ^ts) (cdc6-23) and alpha (polα^ts) (pol1-1) alleles, shown at 28 and 33°C, respectively. The mus81 mutation does not lower the restrictive temperature of a polymerase epsilon (polɛ^ts) (cdc20-m10) allele, shown at 33°C.