The role of human and Drosophila NXF proteins in nuclear mRNA ...

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Introduction 10 The resulting RanGTP gradient allows directionality to importin- and exportin-mediated transport with the high nuclear RanGTP concentration serving as a nuclear marker. Importins bind their substrate in the cytoplasm in the absence of RanGTP and release it in the nucleus after binding of RanGTP. After one round of import, the importin-RanGTP complex is recycled back to the cytoplasm. Conversely, exportin-cargo complexes form only upon RanGTP binding and dissociate in the cytoplasm at low RanGTP concentrations. The empty export receptor is then recycled back to the nucleus (Figure 2). Even though the translocation process per se is not directly coupled to nucleotide hydrolysis, ongoing transport is an energy-consuming task. This energy-dependence has been proposed to originate at least in part from the RanGTP gradient which requires the hydrolysis of GTP by Ran in the cytoplasm. Figure 2: Nuclear import and export mediated by importin β-like transport receptors Importins bind to cargo molecules in the cytoplasm and mediate interactions with the NPC to translocate the import complex into the nucleus. RanGTP in the nucleus binds to the importin and induces cargo release from the complex. The importin–RanGTP complex is recycled to the cytoplasm where RanGTP is displaced from the importin by RanBP1 or RanBP2, followed by RanGAP-induced GTP hydrolysis. An export cycle is similar, the crucial difference being that RanGTP induces cargo binding in the nucleus. Upon removal of RanGTP from the complex and GTP hydrolysis in the cytoplasm, the exportin dissociates from the cargo and the empty receptor recycles back to the nucleus (modified from Kuersten et al., 2001).
1.2 The nuclear export of RNAs Introduction 11 Most classes of RNAs have to be exported to the cytoplasm after their synthesis in the nucleus. These include transcripts synthesized by RNA polymerase I (large rRNAs), RNA polymerase II (mRNAs and most U snRNAs) and RNA polymerase III (e.g. tRNAs, 5S rRNA and U6 snRNA). Microinjection experiments in Xenopus oocytes have shown that different classes of RNA use distinct pathways to exit the nucleus as they competitively inhibit their own export at concentrations at which they have no effect on the export of other classes of RNA (Jarmolowski et al., 1994; Pokrywka and Goldfarb, 1995). This observation is based on the fact that the different classes of RNAs use different soluble transport receptors as described in the following paragraphs. While tRNAs, U snRNAs and rRNAs are exported by members of the importin β-like family, the nuclear export of mRNAs is largely independent of importin β-like family members (Figure 3). A common feature of all RNA export processes is that RNAs are generally transported as ribonucleoprotein complexes (RNPs). 1.2.1 Nuclear export of tRNAs Two different importin β-like family members have been shown to be involved in tRNA export: exportin-t and exportin5 (Arts et al., 1998a; Bohnsack et al., 2002; Kutay et al., 1998; reviewed by: Cullen, 2000; Gorlich and Kutay, 1999; Simos et al., 2002). They are the only known members of the importin β-like family which interact directly with their RNA substrate (i.e. without the help of adapter proteins). Exportin-t binds directly and specifically to tRNAs. This interaction is highly favored by the presence of RanGTP and therefore occurs preferentially in the nucleus (Arts et al., 1998a; Kutay et al., 1998). Exportin-t is believed to interact with nucleoporins allowing the translocation through the nuclear pore. The trimeric exportin-t:tRNA:RanGTP complex dissociates in the cytoplasm upon Ran removal (releasing the tRNA), and exportin-t is recycled back to the nucleus (Kutay et al., 1998). As for all other classes of RNAs, only fully processed ("mature") tRNA molecules reach the cytoplasm. The maturation of eukaryotic tRNAs includes trimming of the 3' and 5' ends of the precursors, modification of nucleosides, addition of the 3' CCA end and, in some cases, the removal of an intron (reviewed in Wolin and Matera, 1999). The maturation is generally believed to be nuclear and has been shown to be a prerequisite for export (De Robertis et al., 1981; Melton et al., 1980). This is in agreement with the fact that exportin-t interacts only very poorly with tRNAs lacking the mature 5' or 3' end or appropriate modifications (Arts et al., 1998b; Kutay et al., 1998; Lipowsky et al., 1999). However, exportin-t can bind and export tRNAs containing an intron when both exportin-t and the intron-containing tRNA are injected into Xenopus oocytes (Arts et al., 1998b;
Page 1 and 2: The role of human and Drosophila NX
Page 3 and 4: This thesis describes work carried
Page 5 and 6: Table of Contents Table of Contents
Page 7 and 8: Summary Summary 1 A distinguishing
Page 9 and 10: Summary 3 Crm1 resulted in decrease
Page 11 and 12: Zusammenfassung 5 NXF1 durch RNAi v
Page 13 and 14: 1 Introduction 1.1 Nucleocytoplasmi
Page 15: 1.1.4 The importin ββ-like family
Page 19 and 20: Introduction 13 with the export of
Page 21 and 22: Introduction 15 What are the critic
Page 23 and 24: Introduction 17 mRNA export are ind
Page 25 and 26: Introduction 19 The NPC-binding dom
Page 27 and 28: Introduction 21 Association of the
Page 29 and 30: Introduction 23 could trigger ATP-d
Page 31 and 32: Introduction 25 Sub2p and Yra1p and
Page 33 and 34: Introduction 27 In S. cerevisiae, s
Page 35 and 36: Introduction 29 export block of bul
Page 37 and 38: Introduction 31 efficiently blocks
Page 39 and 40: 2 Results/Publications Results/Publ
Page 41 and 42: Results/Publications 35 shown to in
Page 43 and 44: VOL. 20, 2000 NXF MULTIGENE FAMILY
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Page 55 and 56: Results/Publications 49 2.1.2 Paper
Page 57 and 58: Research Paper 1381 NXF5, a novel m
Page 59 and 60: Research Paper Loss of the NXF5 gen
Page 63 and 64: Figure 4 Research Paper Loss of the
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Research Paper Loss of the NXF5 gen
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Results/Publications 63 with the nu
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RNA (2001), 7:1768-1780+ Cambridge
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1770 A. Herold et al. FIGURE 1. Com
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1772 A. Herold et al. FIGURE 3. Dep
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1774 A. Herold et al. FIGURE 5. Dep
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1776 A. Herold et al. FIGURE 7. hsp
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1778 A. Herold et al. 2001)+ Simila
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1780 A. Herold et al. Black BE, Hol
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Results/Publications 79 mRNAs had a
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Herold et al. Results/Publications
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Herold et al. (Supplemental Materia
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Herold et al. (Supplemental Materia
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A 10000 reference 1000 100 10 10000
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A 10 1 -10 3.07 (11) 2.37 4.74 (20)
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A B Northern blot dsRNA sd06908: cl
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GFP day4 NXF1 day2 NXF1 day4 p15 da
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Supplemental Table I. mRNAs not aff
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GH06306 1.86 1.49 2.60 1.65 2.95 2.
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Supplemental Table III: mRNAs that
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Supplemental Table IV: mRNAs that a
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2.3 Functional analysis of TAP/NXF1
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THE JOURNAL OF BIOLOGICAL CHEMISTRY
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20538 FIG. 1. Domain organization o
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20540 FIG. 4. TAP stimulates export
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20542 CRM1-mediated export of U snR
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Results/Publications 127 2.3.2 Pape
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MOLECULAR AND CELLULAR BIOLOGY, Aug
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VOL. 22, 2002 p15-INDEPENDENT NUCLE
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Results/Publications 143 2.4 Role o
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The EMBO Journal Vol. 21 No. 20 pp.
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B.M.H.Lange et al. somes at metapha
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B.M.H.Lange et al. Fig. 5. Aurora B
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B.M.H.Lange et al. Fig. 6. Aurora B
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B.M.H.Lange et al. released along t
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B.M.H.Lange et al. protein kinase i
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Discussion 157 strain, already poin
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Discussion 159 by a (second) UBA-li
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Discussion 161 gradual process requ
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Discussion 163 Although there is no
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Discussion 165 identify mRNAs which
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Human NXFs Discussion 167 While the
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Discussion 169 Therefore, DmNXF1 sh
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References References 171 Aitchison
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References 173 Gadal, O., Strauss,
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References 175 Katahira, J., Strass
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References 177 Murphy, R., Watkins,
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References 179 Strasser, K., Masuda
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Abbreviations Abbreviations 181 ARE
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Curriculum vitae Personal Details N
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Erklärung Hiermit erkläre ich ehr
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