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Charakterisierung des mRNA-Exportweges bei zellulärem Stress in Saccharomyces cerevisiae

dc.contributor.advisorKrebber, Heike Prof. Dr.
dc.contributor.authorBender, Lysann
dc.titleCharakterisierung des mRNA-Exportweges bei zellulärem Stress in Saccharomyces cerevisiaede
dc.title.translatedAnalyses of the mRNA export pathway in Saccharomyces cerevisiae under cellular stressde
dc.contributor.refereeKrebber, Heike Prof. Dr.
dc.description.abstractengIn response to stress cells activate a prompt expression of stress-specific genes of which chaperones are essential in stabilizing and refolding proteins. In this situation stress-specific RNAs are selectively transcribed, exported and translated while these processes for regular mRNAs are repressed. The aim of this study was to investigate the mechanisms that suppresses regular mRNA export from the nucleus to the cytoplasm during stress and allow selective transport of stress specific mRNAs. RNA-co-immunoprecipitation (RIP) experiments revealed that binding of the general mRNA adapter proteins Npl3, Gbp2, Hrb1 and Nab2 and the export receptor Mex67-Mtr2 for poly(A)+RNA is strongly reduced in Saccharomyces cerevisiae under cellular stress which consequently leads to a loss of transport competence and prevents nuclear export. Nuclear export of stress specific mRNAs (SSA4 and HSP12) was analyzed by RNA fluorescence in situ hybridization (RNA-FISH) experiments in mutant strains of the mRNA export factors. In contrast to regular mRNA stress specific RNAs are bound by the export receptor Mex67-Mtr2 but not by the adapter proteins (Npl3, Gbp2, Hrb1 and Nab2) indicating the sufficiency of Mex67-Mtr2 for export competence. This was further proved via direct binding of Mex67-Mtr2 to regular and stress specific transcripts without the need of adapter proteins shown by in vitro RNA-binding studies. Interestingly the binding of Mex67 to mRNA is established by its loop-domain. In contrast to exported regular mRNAs Mex67 remains bound on cytoplasmic stress-specific transcripts during heat shock as Mex67 co-precipitates with polysomes shown by sucrose density centrifugation experiments. Based on the difference between the mRNA export modes (normal condition and stress) the question arises why binding of the adapter proteins to regular mRNA is useful, taking into account that the export receptor Mex67-Mtr2 can bind directly. A possible explanation might be a function of the mRNA adapter proteins in the quality control of regular mRNAs while stress specific transcripts undergo no control before nuclear export. Within the quality control process the adapter proteins prevent presumably an early binding of the mRNA export receptor to the mRNA. This study could show that unprocessed stress specific transcripts are not accumulated in mRNA quality control mutants indicating the fast export of stress specific mRNAs without the need for the quality control mechanism. This was analyzed by FISH experiments. Furthermore this study demonstrates that the promoter region within the RNA determines whether a transcript undergoes quality control or not. This was supported by converting the regular mRNA into a stress-responsive transcript by fusing the open reading frame of CYC1 with the heat shock promoter HSP12. In summary RNA adapter proteins play a role in mRNA surveillance under normal conditions and prevent an early association of the export receptor Mex67-Mtr2. However, during stress, quality control is bypassed and Mex67 could be instead directly recruited to heat-responsive genes and loaded onto the stress-specific transcripts for instant nuclear
dc.contributor.coRefereeBraus, Gerhard Prof. Dr.
dc.subject.engmRNA export pathwayde
dc.subject.engexport receptorde
dc.affiliation.instituteBiologische Fakultät für Biologie und Psychologiede
dc.subject.gokfullBiologie (PPN619462639)de

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