Limits...
Structural basis for the assembly and nucleic acid binding of the TREX-2 transcription-export complex.

Ellisdon AM, Dimitrova L, Hurt E, Stewart M - Nat. Struct. Mol. Biol. (2012)

Bottom Line: Sac3-Thp1-Sem1 forms a previously uncharacterized PCI-domain complex characterized by the juxtaposition of Sac3 and Thp1 winged helix domains, forming a platform that mediates nucleic acid binding.Our structure-guided mutations support the idea that the Thp1-Sac3 interaction is an essential requirement for mRNA binding and for the coupling of transcription and processing to mRNP assembly and export.These results provide insight into how newly synthesized transcripts are efficiently transferred from TREX-2 to the principal mRNA export factor, and they reveal how Sem1 stabilizes PCI domain-containing proteins and promotes complex assembly.

View Article: PubMed Central - PubMed

Affiliation: Medical Research Council Laboratory of Molecular Biology, Cambridge, UK.

ABSTRACT
The conserved TREX-2 transcription-export complex integrates transcription and processing of many actively transcribed nascent mRNAs with the recruitment of export factors at nuclear pores and also contributes to transcriptional memory and genomic stability. We report the crystal structure of the Sac3-Thp1-Sem1 segment of Saccharomyces cerevisiae TREX-2 that interfaces with the gene expression machinery. Sac3-Thp1-Sem1 forms a previously uncharacterized PCI-domain complex characterized by the juxtaposition of Sac3 and Thp1 winged helix domains, forming a platform that mediates nucleic acid binding. Our structure-guided mutations support the idea that the Thp1-Sac3 interaction is an essential requirement for mRNA binding and for the coupling of transcription and processing to mRNP assembly and export. These results provide insight into how newly synthesized transcripts are efficiently transferred from TREX-2 to the principal mRNA export factor, and they reveal how Sem1 stabilizes PCI domain-containing proteins and promotes complex assembly.

Show MeSH
Schematic illustration of how the TREX-2 complex integrates the formation of an export competent mRNP adjacent to NPCs. The proximal region of Sac3 to which Sus1 and Cdc31 are attached binds to components of the nuclear basket such as Nup1 whereas the distal region that contains the winged helix domains of Sac3 and Thp1 binds to mRNA, to which Yra1–Sub2 is also attached. The Mex67–Mtr2 nuclear export factor binds to the FG repeats in the distal region of Sac3, probably via its NTF2 and UBA domains that bind to FG-nucleoporins. This interaction brings the Mex67 LRR and RNP domains close to the mRNA, facilitating the Sub2-mediated remodeling that generates an export-competent mRNP close to the NPC.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3303126&req=5

Figure 6: Schematic illustration of how the TREX-2 complex integrates the formation of an export competent mRNP adjacent to NPCs. The proximal region of Sac3 to which Sus1 and Cdc31 are attached binds to components of the nuclear basket such as Nup1 whereas the distal region that contains the winged helix domains of Sac3 and Thp1 binds to mRNA, to which Yra1–Sub2 is also attached. The Mex67–Mtr2 nuclear export factor binds to the FG repeats in the distal region of Sac3, probably via its NTF2 and UBA domains that bind to FG-nucleoporins. This interaction brings the Mex67 LRR and RNP domains close to the mRNA, facilitating the Sub2-mediated remodeling that generates an export-competent mRNP close to the NPC.

Mentions: Our data support a model whereby NPC-bound TREX-2 acts as a scaffold to spatially integrate transcription and mRNA export and provides a structural context for how this could be achieved (Fig. 6). TREX-2 comprises two subregions that make different contributions to its function. Whereas the localization of TREX-2 to NPCs requires its proximal CID domain complexed with Cdc31 and two Sus1 chains13,22, its interaction with the transcription and mRNP assembly machinery is mediated by its distal N- and M-regions21 that bind Thp1–Sem1 and Mex67–Mtr2. Deletion of thp1 or sem1 results in mRNA export defects and generation of mRNPs with elevated Yra1 and Sub2 levels23. These observations, together with the synthetic growth defects observed between TREX-2 mutants with impaired nucleic acid binding and the mex67-5 or yra1-ΔRRM alleles (Fig. 5f), are consistent with the distal region of TREX-2 functioning to load Mex67–Mtr2 and generate export-competent mRNPs23. Mex67–Mtr2 by itself has low affinity for mRNA and its recruitment to mRNPs and generation of export-competent complexes requires Yra1 (refs 1,3). Mex67–Mtr2 binds to the Sac3 N-terminus adjacent to Thp1–Sem1 probably through its NTF2-like and UBA domains binding to Sac3 FG-nup-like repeats21. As illustrated in Figure 6, tethering an mRNA transcript already loaded with Yra1 and Sub2 to the winged helix domains of Sac3 and Thp1 would bring it in close proximity to the Mex67–Mtr2 heterodimer, promoting the generation of an export-competent mRNP in the immediate vicinity of the pore, thereby increasing the rate of mRNA export.


Structural basis for the assembly and nucleic acid binding of the TREX-2 transcription-export complex.

Ellisdon AM, Dimitrova L, Hurt E, Stewart M - Nat. Struct. Mol. Biol. (2012)

Schematic illustration of how the TREX-2 complex integrates the formation of an export competent mRNP adjacent to NPCs. The proximal region of Sac3 to which Sus1 and Cdc31 are attached binds to components of the nuclear basket such as Nup1 whereas the distal region that contains the winged helix domains of Sac3 and Thp1 binds to mRNA, to which Yra1–Sub2 is also attached. The Mex67–Mtr2 nuclear export factor binds to the FG repeats in the distal region of Sac3, probably via its NTF2 and UBA domains that bind to FG-nucleoporins. This interaction brings the Mex67 LRR and RNP domains close to the mRNA, facilitating the Sub2-mediated remodeling that generates an export-competent mRNP close to the NPC.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3303126&req=5

Figure 6: Schematic illustration of how the TREX-2 complex integrates the formation of an export competent mRNP adjacent to NPCs. The proximal region of Sac3 to which Sus1 and Cdc31 are attached binds to components of the nuclear basket such as Nup1 whereas the distal region that contains the winged helix domains of Sac3 and Thp1 binds to mRNA, to which Yra1–Sub2 is also attached. The Mex67–Mtr2 nuclear export factor binds to the FG repeats in the distal region of Sac3, probably via its NTF2 and UBA domains that bind to FG-nucleoporins. This interaction brings the Mex67 LRR and RNP domains close to the mRNA, facilitating the Sub2-mediated remodeling that generates an export-competent mRNP close to the NPC.
Mentions: Our data support a model whereby NPC-bound TREX-2 acts as a scaffold to spatially integrate transcription and mRNA export and provides a structural context for how this could be achieved (Fig. 6). TREX-2 comprises two subregions that make different contributions to its function. Whereas the localization of TREX-2 to NPCs requires its proximal CID domain complexed with Cdc31 and two Sus1 chains13,22, its interaction with the transcription and mRNP assembly machinery is mediated by its distal N- and M-regions21 that bind Thp1–Sem1 and Mex67–Mtr2. Deletion of thp1 or sem1 results in mRNA export defects and generation of mRNPs with elevated Yra1 and Sub2 levels23. These observations, together with the synthetic growth defects observed between TREX-2 mutants with impaired nucleic acid binding and the mex67-5 or yra1-ΔRRM alleles (Fig. 5f), are consistent with the distal region of TREX-2 functioning to load Mex67–Mtr2 and generate export-competent mRNPs23. Mex67–Mtr2 by itself has low affinity for mRNA and its recruitment to mRNPs and generation of export-competent complexes requires Yra1 (refs 1,3). Mex67–Mtr2 binds to the Sac3 N-terminus adjacent to Thp1–Sem1 probably through its NTF2-like and UBA domains binding to Sac3 FG-nup-like repeats21. As illustrated in Figure 6, tethering an mRNA transcript already loaded with Yra1 and Sub2 to the winged helix domains of Sac3 and Thp1 would bring it in close proximity to the Mex67–Mtr2 heterodimer, promoting the generation of an export-competent mRNP in the immediate vicinity of the pore, thereby increasing the rate of mRNA export.

Bottom Line: Sac3-Thp1-Sem1 forms a previously uncharacterized PCI-domain complex characterized by the juxtaposition of Sac3 and Thp1 winged helix domains, forming a platform that mediates nucleic acid binding.Our structure-guided mutations support the idea that the Thp1-Sac3 interaction is an essential requirement for mRNA binding and for the coupling of transcription and processing to mRNP assembly and export.These results provide insight into how newly synthesized transcripts are efficiently transferred from TREX-2 to the principal mRNA export factor, and they reveal how Sem1 stabilizes PCI domain-containing proteins and promotes complex assembly.

View Article: PubMed Central - PubMed

Affiliation: Medical Research Council Laboratory of Molecular Biology, Cambridge, UK.

ABSTRACT
The conserved TREX-2 transcription-export complex integrates transcription and processing of many actively transcribed nascent mRNAs with the recruitment of export factors at nuclear pores and also contributes to transcriptional memory and genomic stability. We report the crystal structure of the Sac3-Thp1-Sem1 segment of Saccharomyces cerevisiae TREX-2 that interfaces with the gene expression machinery. Sac3-Thp1-Sem1 forms a previously uncharacterized PCI-domain complex characterized by the juxtaposition of Sac3 and Thp1 winged helix domains, forming a platform that mediates nucleic acid binding. Our structure-guided mutations support the idea that the Thp1-Sac3 interaction is an essential requirement for mRNA binding and for the coupling of transcription and processing to mRNP assembly and export. These results provide insight into how newly synthesized transcripts are efficiently transferred from TREX-2 to the principal mRNA export factor, and they reveal how Sem1 stabilizes PCI domain-containing proteins and promotes complex assembly.

Show MeSH