Stress response in yeast mRNA export factor: reversible changes in Rat8p localization are caused by ethanol stress but not heat shock.

Reiko Takemura,Yoshiharu Inoue,Shingo Izawa

doi:10.1242/jcs.01296

Abstract

Ethanol stress (10% v/v) causes selective mRNA export in Saccharomyces cerevisiae in a similar manner to heat shock (42 degrees C). Bulk poly(A)(+) mRNA accumulates in the nucleus, whereas heat shock protein mRNA is exported under such conditions. Here we investigated the effects of stress on mRNA export factors. In cells treated with ethanol stress, the DEAD box protein Rat8p showed a rapid and reversible change in its localization, accumulating in the nucleus. This change correlated closely with the blocking of bulk poly(A)(+) mRNA export caused by ethanol stress. We also found that the nuclear accumulation of Rat8p is caused by a defect in the Xpo1p/Crm1p exportin. Intriguingly, the localization of Rat8p did not change in heat shocked cells, suggesting that the mechanisms blocking bulk poly(A)(+) mRNA export differ for heat shock and ethanol stress. These results suggest that changes in the localization of Rat8p contribute to the selective export of mRNA in ethanol stressed cells, and also indicate differences in mRNA export between the heat shock response and ethanol stress response.

Highlights

In eukaryotic cells, mRNA is synthesized and processed in the nucleus and exported to the cytoplasm through nuclear pore complexes (NPCs)
In Saccharomyces cerevisiae, matured mRNA is exported as messenger ribonucleoprotein complexes by mRNA export factors including RNA binding proteins (Sub2p, Mud2p, Yra1p, Yra2p, Mex67p, Npl3p, Nab2p and Hrp1p), nucleoporins and NPC-associated proteins (Mtr2p, Gle1p, Gle2p, Rip1p/Nup42p and Rat7p/Nup159p) and DEAD box RNA helicase (Rat8p/Dbp5p)
We found that the localization of Rat8p/Dbp5p, an essential mRNA export factor, changed in ethanol stressed cells

Summary

Introduction

MRNA is synthesized and processed in the nucleus and exported to the cytoplasm through nuclear pore complexes (NPCs). Several studies show that polyadenylation during 3′-end processing is coupled to the efficient export of mRNA (Hilleren et al, 2001; Jensen et al, 2001; Hammell et al, 2002; Lei and Silver, 2002b). Both hyperadenylation and defects in polyadenylation lead to the blocking of mRNA export and the apparent accumulation of pre-mRNA at the site of transcription (Brodsky and Silver, 2000; Jensen et al, 2001). Several mutant strains defective in mRNA export exhibit hyperadenylation of the 3′-end of mRNA (Hilleren and Parker, 2001)

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Conclusion