FIG. 3.

rad9⁺ acts downstream of rad12⁺ in the repression of basal levels of UVDE activity. (a) Cells were grown to late log phase and then treated with UV where indicated. Cells were allowed to recover for the indicated time periods and then harvested, and whole-cell extracts were prepared. The extracts were assayed for UVDE activity, as measured by cleavage of an oligonucleotide substrate with a single internal UV photoproduct from a 51mer to a 31mer. WT, wild type. (b) Basal levels of uve1⁺ mRNA were determined by Northern analysis in wild-type and rad9 null cells. Samples were subjected to electrophoresis, transfer, and hybridization against uve1⁺ and leu1⁺ probes simultaneously. (c) Time course of uve1⁺ mRNA induction in wild-type (972) and rad9 null (Sp325) cells after treatment with 50 J of UV light/m². Inductions were performed as described in Materials and Methods. Cells were harvested at the indicated times (in minutes) after induction. Poly(A)⁺ RNA was subjected to Northern analysis with probes directed against uve1⁺ and leu1⁺. (d) UVDE activity was assayed as for panel a, using strains rad12-502 (Sp275) (lane 3), rad9::ura4⁺ (Sp325) (lane 2), and rad12-502 rad9::ura4⁺ (Sp345) (lane 1) mutants.