RPN4 and PDR1 are dependent on each other for regulation by selenite. The levels of expression of PDR1 (upper panel) and RPN4 (lower panel) after selenite or mock treatment were quantified in wild-type and rpn4Δ (upper panel) or pdr1Δ (lower panel) cells, using real-time quantitative PCR. The expression values were normalized using the gene encoding actin (ACT1, see methods). The values represented here are the ratios of the normalized expression levels of PDR1 (upper panel) or RPN4 (lower panel) in the presence of selenite, versus the normalized expression levels of these genes in mock experiments. Each measurement was repeated three times on independent samples. The standard errors are indicated.