Regulation of mRNA export in response to stress in Saccharomyces cerevisiae

The response of eukaryotic cells to heat shock and other forms of stress occurs at both transcriptional and post-transcriptional levels. We used in situ hybridization to determine whether stress affected the subcellular distribution of poly(A)(+) RNA in Saccharomyces cerevisiae. Following induction of stress by either heat shock (42 degrees C) or addition of a high concentration of ethanol (10%), the nucleocytoplasmic export of most poly(A)(+) RNA was blocked. In situ hybridization indicated that heat-inducible SSA4 and SSA1 mRNAs were exported from nuclei under these same conditions. On the other hand, both GAL1 and URA3 transcripts expressed from the SSA4 promoter accumulated in nuclei following heat shock. Sequences within either the 5' 1600 or the 3' 500 nucleotides of SSA4 mRNA were sufficient to direct GAL1 mRNA to the cytoplasm during stress. The export of SSA4 mRNA following stress required functional nuclear pore complexes, as SSA4 mRNA accumulated in nuclei following heat shock of cells containing temperature-sensitive nucleoporins. However, the selective export of SSA4 mRNA was maintained in heat-shocked cells carrying temperature-sensitive alleles of RNA1, PRP20, or an inducible dominant-negative allele of GSP1, the S. cerevisiae homolog of RAN/TC4. The results reported here suggest that there is selective export of mRNA in yeast.