As another peptidyl-prolyl isomerase, Ess1, has been shown to regulate Ser5-P of RNAPII at the end of snRNAs genes, thereby promoting transcription termination via the Nrd1 pathway. In addition, over expression of Pin1 results in hyper phosphorylation of RNAPII and its release from the chromatin. It is known that RNAPII occupancy is regulated during transcription elongation, for example, it was previously reported that RNAPII was enriched on ribosomal genes but associated with a slow transcriptional rate. Interestingly, when these cells were transferred from glucose to galactose containing medium, the level of RNAPII AbMole Mepiroxol decreased on these ribosomal genes and their transcriptional rate increased. Simultaneously, RNAPII was recruited to other genes including those involved in mitochondrial function. Similar to a switch from glucose to galactose, AbMole Riociguat BAY 63-2521 rapamycin induces a transcriptional response which requires some genes to be turned off and others to be induced. Rrd1 might promote this transcriptional reorganization by allowing Ser5-P and Ser2-P changes thereby fine-tuning the elongation efficiency. Based on our model, we predicted that Rrd1 might play a similar role in other stress response situations, notably the environmental stress responses that induce a similar pattern of gene expression as rapamycin. Indeed, rrd1D mutants are sensitive to agents that cause oxidative stress, which is known to induce a drastic transcriptional response. Although these phenotypes may at first glance seem opposite of the one observed for rapamycin, they are actually consistent with our model of Rrd1 function: In both cases, the response to the stress condition is inhibited in rrd1D cells. This leads to resistance to rapamycin, but sensitivity to oxidative stress. In accordance with this, we show that Rrd1 is required to adequately induce gene expression on a subset of stress responsive genes upon various stress conditions. Surprisingly, ribosomal genes were not strongly downregulated in wild-type cells as predicted from the ChIP-chip data. Since mRNA levels were measured at 30 min, long mRNA half-lives could obscure the drop in transcription that was apparent in the ChIP-chip data. Rrd1 was required for induction of stress-induced genes, however, consistent with our model. Interestingly, rrd1D cells showed stronger defects for some stresses than others. For example, HSP12 induction was dependent on Rrd1 after rapamycin and H2O2, but not heat shock and to a lesser extend with NaAs. This might be due to effects specific to each condition, as not all of the genes we tested were induced in the same manner by each condition. For example, the NaAs exporter ACR3 was only expressed in response to NaAs, and this was dependent on Rrd1 despite the fact that expression was specific to one condition. Taken together, we have shown that Rrd1 regulates the transcriptional stress response via two mechanisms, through regulation of PIC assembly, and more drastically through regulation of RNAPII elongation.