Transcription factors Pcr1 and Atf1 have distinct roles in stress- and Sty1-dependent gene regulation

The mitogen-activated protein kinase Sty1 is essential for the regulation of transcriptional responses that promote cell survival in response to different types of environmental stimuli in Schizosaccharomyces pombe. Upon stress activation, Sty1 reversibly accumulates in the nucleus, where it stimulates gene expression via the Atf1 transcription factor. The Atf1 protein forms a heterodimer with Pcr1, but the specific role of this association is controversial. We have carried out a comparative analysis of strains lacking these proteins individually. We demonstrate that Atf1 and Pcr1 have similar but not identical roles in S. pombe, since cells lacking Pcr1 do not share all the phenotypes reported for Delta atf1 cells. Northern blot and microarray analyses demonstrate that the responses to specific stresses of cells lacking either Pcr1 or Atf1 do not fully overlap, and even though most Atf1-dependent genes induced by osmotic stress are also Pcr1 dependent, a subset of genes require only the presence of Atf1 for their induction. Whereas binding of Atf1 to most stress-dependent genes requires the presence of Pcr1, we demonstrate here that Atf1 can bind to the Pcr1-independent promoters in a Delta pcr1 strain in vivo. Furthermore, these analyses show that both proteins have a global repressive effect on stress-dependent and stress-independent genes.