The stress-activated MAP kinase Sty1/Spc1 and a 3'-regulatory element mediate UV-induced expression of the uvi15(+) gene at the post-transcriptional level

A sequence element downstream of the yeast HTB1 gene contributes to mRNA 3' processing and cell cycle regulation

Histone mRNAs accumulate in the S phase and are rapidly degraded as cells progress into the G(2) phase of the cell cycle. In Saccharomyces cerevisiae, fusion of the 3' untranslated region and downstream sequences of the yeast histone gene HTB1 to a neomycin phosphotransferase open reading frame is sufficient to confer cell cycle regulation on the resulting chimera gene (neo-HTB1). We have identified a sequence element, designated the distal downstream element (DDE), that influences both the 3'-end cleavage site selection and the cell cycle regulation of the neo-HTB1 mRNA. Mutations in the DDE, which is located approximately 110 nucleotides downstream of the HTB1 gene, lead to a delay in the accumulation of the neo-HTB1 mRNA in the S phase and a lack of mRNA turnover in the G(2) phase. The DDE is transcribed as part of the primary transcript and binds a protein factor(s). Maximum binding is observed in the S phase of the cell cycle, and mutations that affect the turnover of the HTB1 mRNA alter the binding activity. While located in the same general region, mutations that affect 3'-end cleavage site selection act independently from those that alter the cell cycle regulation.

Fibrillarin binds to a 3' cis-regulatory element in pre-mRNA of uvi15+ in fission yeast

uvi15+ is induced by various stresses including exposure to UV-light. Previously, we demonstrated that the UV-induction is mainly regulated at the post-transcriptional level through a cis-acting element in the pre-mRNA. Here we show that deletion analyses define an 18-nt element responsible for the UV-induction. RNA gel mobility shift assay showed that a specific protein(s) could form a complex with the 54-nt element but its binding ability is moderately decreased in response to UV-light. Using yeast three-hybrid screen, we isolated a homolog of fibrillarin as a protein interacting with the 54-nt element, which is a key nucleolar protein for pre-rRNA processing. We further showed that the recombinant fibrillarin specifically binds to the element in a sequence-specific manner. Thus, the data suggest that fission yeast fibrillarin might regulate uvi15+ mRNA stability via binding with the 54-nt element in the pre-mRNA, implying that fibrillarin is involved in both pre-mRNA and pre-rRNA processing.

Glucose-inducible expression of rrg1+ in Schizosaccharomyces pombe: post-transcriptional regulation of mRNA stability mediated by the downstream region of the poly(A) site

rrg1+(rapid response to glucose) has been isolated previously as a UV-inducible gene in Schizosaccharomyces pombe, designated as uvi22+. However, it was revealed that the transcript level of this gene was regulated by glucose, not by DNA-damaging agents. Glucose depletion led to a rapid decrease in the level of rrg1+ mRNA, by approximately 50% within 30 min. This effect was readily reversed upon re-introduction of glucose within 1 h. High concentrations (4 and 8%) of glucose showed similar effects on increasing the rrg1+ mRNA level compared with 2% glucose, while a low concentration (0.1%) was not effective in raising the rrg1+ mRNA level. In addition, sucrose and fructose could increase rrg1+ mRNA level. Interestingly, the rapid decline in mRNA level seen upon glucose deprivation resulted from precipitous reduction of mRNA half-life. Serial and internal deletions within the 3'-flanking region of rrg1+ revealed that a 210-nt region downstream of the distal poly(A) site was critical for glucose-regulated expression. Moreover, this downstream region participated in 3'-end formation of mRNA. Taken together, this is the first report on glucose-inducible expression regulated post-transcriptionally by control of mRNA stability in S.pombe.