Exposure of Schizosaccharomyces pombe cells to UV light results in increased uvi15+ gene expression at both the mRNA and protein levels, leading to elevated cell survival. This UV-induced expression of the uvi15+ gene was reduced in Δsty1 and Δwis1 cells lacking the stress-activated protein kinase pathway, but not in DNA damage checkpoint mutants. To further understand the cellular mechanisms responsible for this UV-induced expression, the transcription rate and mRNA half-life were investigated. Transcription run-on assays revealed that the rate of uvi15+ transcription was increased 1.8-fold regardless of Sty1 when cells were UV irradiated. The half-life of uvi15+ mRNA was also increased 1.5-fold after UV irradiation, but it was decreased in the Δsty1 background for both basal and UV-induced mRNAs, indicating that the stress-activated MAPK cascade can mediate UV-induced gene expression by increasing mRNA half-life. Deletion analyses identified a 54 nt element downstream of the distal poly(A) site, which was involved in the increased half-life of uvi15+ mRNA. These results suggest that both Sty1 and the 3'-regulatory element regulate UV-induced expression of the uvi15+ gene at the post-transcriptional level.
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