THE UV RESPONSE INVOLVING THE RAS SIGNALING PATHWAY AND AP-1 TRANSCRIPTION FACTORS IS CONSERVED BETWEEN YEAST AND MAMMALS

UV irradiation of mammalian cells activates AP-1 through a Ras-depende nt pathway, independently of DNA damage. We show that the yeast S. cer evisiae has a remarkably similar UV response involving the AP-1 factor Gcn4, which is distinct from the DNA damage response. Transcriptional activation of HIS3 and HIS4 by Gcn4 is triggered by UV irradiation in a Ras-dependent fashion. Moreover, resistance of yeast to UV irradiat ion is correlated with the level of Ras activity and Gcn4 function. Li ke mammalian cells in which activated Ras leads to increased c-Jun syn thesis and phosphorylation, the effects in yeast involve increased tra nslation of GCN4 mRNA and a posttranslational event. However, this eff ect on GCN4 translation is different from the response to amino acid o r purine starvation. Therefore, a UV signaling pathway involving Ras a nd AP-1 is an ancient and universal mechanism involved in protection a gainst damage to cellular components other than DNA.