Protein levels of the stress transcription factors Atf1 and Pcr1 depend on the U₃₄ modifying activities Sin3/Elp3 and Ctu2.

<p>(A) Scheme illustrating the activation of the stress gene expression program by Atf1 and Pcr1 (see text for details). (B and C) Absence of Sin3/Elp3 or Ctu2 barely affects transcription of the <i>atf1</i> and <i>pcr1</i> genes but largely affects Atf1 and Pcr1 protein levels. Rich media cultures of strains 972 (WT), IV16 (Δ<i>sin3/elp3</i>) and IV86 (Δ<i>ctu2</i>) treated with 1 mM H₂O₂ at the indicated time points were analyzed to determine transcription levels of <i>atf1</i> and <i>pcr1</i> genes by Northern blot (B), or Atf1 and Pcr1 protein levels by Western blot using polyclonal antibodies (C). <i>act1</i> mRNA or tubulin were used as loading controls for B and C, respectively. (D) Quantification of the relative mRNA and protein levels for <i>atf1</i>, <i>pcr1</i>, Atf1 and Pcr1 in wild-type and mutant strains. The Northern or Western blot panels of experiments as in B and C, respectively, were quantified and represented here relative to untreated wild-type levels (with an assigned value of 1). The <i>atf1</i> and <i>pcr1</i> mRNA levels normalized to <i>act1</i> are shown in the left two panels, <i>w</i>hereas the Atf1 and Pcr1 protein levels normalized to tubulin are shown in the two right panels. Error bars (SEM) were calculated from biological duplicates.