Co-translational localization of an LTR-retrotransposon RNA to the endoplasmic reticulum nucleates virus-like particle assembly sites.
Co-translational localization of an LTR-retrotransposon RNA to the endoplasmic reticulum nucleates virus-like particle assembly sites.
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DOI：
10.1371/journal.pgen.1004219
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发表时间：
2014-03
期刊：
影响因子：
4.5
通讯作者：
Curcio MJ
中科院分区：
文献类型：
--
作者：
Doh JH;Lutz S;Curcio MJ
逆转录病毒样转座子的转录本作为衣壳和复制蛋白合成的mRNA和病毒样颗粒（vlp）的基因组RNA，其中基因组被复制。逆转录转座子RNA和蛋白质在细胞质焦点或逆转录体中结合，以启动VLP组装，但逆转录体如何成核尚不清楚。我们确定了酿酒酵母Ty1反转录转座子的RNA和Gag蛋白是如何定向到逆转录体的。我们发现Ty1 RNA与信号识别颗粒（SRP）相关，SRP是一种普遍保守的伴侣，结合特定的核糖体-新生链（RNC）复合物并将新生肽靶向内质网（ER）。Gag被转移到ER管腔；然而，它也存在于细胞质中，与SRP-RNC复合物有关。在没有ER易位的情况下，Gag被合成但迅速降解，Ty1 RNA在逆转录体中不合并。这些发现表明Gag在内质网腔中采用稳定的构象，逆转录到细胞质中，与SRP-RNC复合物上的Ty1 RNA结合并聚合成核逆转录体。与该模型一致，我们发现通过限制SRP来减缓共翻译ER易位的速度会增加反转录体的患病率，而通过减缓翻译延伸来抑制SRP次形易位缺陷会迅速减少反转录体的形成。因此，逆转录体是Ty1 RNA-RNC复合物的动态焦点，其形成受共翻译ER易位率的调节。总之，这些发现表明，翻译Ty1 mRNA和VLP的基因组RNA起源于一个单一的池，此外，Ty1 RNA的共翻译定位形成了假定的VLP组装位点。通过ER转运将新生Gag从其RNA模板中分离，使Gag能够结合翻译的Ty1 RNA，而不会对其编码RNA表现出顺式偏好。反转录转座子是一种可移动的元件，侵入了从细菌到人类的生物体的基因组。在宿主辅助因子的促进下，逆转录转座子蛋白将其RNA基因组复制成整合到宿主基因组中的DNA，导致突变和基因组不稳定。酵母Ty1元素属于与传染性逆转录病毒有关的反转录转座子家族。Ty1 RNA及其外壳蛋白Gag组装成病毒样颗粒，其中RNA被复制成DNA。以前不知道Ty1 RNA和Gag如何在特定的细胞位置集中，从而启动病毒样颗粒的组装。在这项研究中，我们发现Ty1 RNA在翻译过程中被蛋白伴侣（信号识别粒子）带到假定的组装位点。当Ty1 RNA被翻译时，新生的Gag多肽进入内质网腔，Gag在腔内形成稳定的构象，然后返回细胞质与翻译的Ty1 RNA结合。与翻译Ty1 RNA结合的Gag分子之间的相互作用导致病毒样颗粒组装位点的成核。我们的研究发现了反转录转座子迁移的新宿主辅助因子，并提出了控制衰老和癌症中反转录转座子相关基因组不稳定性的潜在方法。
The transcript of retrovirus-like transposons functions as an mRNA for synthesis of capsid and replication proteins and as the genomic RNA of virus-like particles (VLPs), wherein the genome is replicated. Retrotransposon RNA and proteins coalesce in a cytoplasmic focus, or retrosome, to initiate VLP assembly, but it is not known how the retrosome is nucleated. We determined how the RNA and Gag protein of the Saccharomyces cerevisiae Ty1 retrotransposon are directed to the retrosome. We found that Ty1 RNA is translated in association with signal recognition particle (SRP), a universally conserved chaperone that binds specific ribosome-nascent chain (RNC) complexes and targets the nascent peptide to the endoplasmic reticulum (ER). Gag is translocated to the ER lumen; yet, it is also found in the cytoplasm, associated with SRP-RNC complexes. In the absence of ER translocation, Gag is synthesized but rapidly degraded, and Ty1 RNA does not coalesce in retrosomes. These findings suggest that Gag adopts a stable conformation in the ER lumen, is retrotranslocated to the cytoplasm, binds to Ty1 RNA on SRP-RNC complexes and multimerizes to nucleate retrosomes. Consistent with this model, we show that slowing the rate of co-translational ER translocation by limiting SRP increases the prevalence of retrosomes, while suppressing the translocation defect of srp hypomorphs by slowing translational elongation rapidly decreases retrosome formation. Thus, retrosomes are dynamic foci of Ty1 RNA-RNC complexes whose formation is modulated by the rate of co-translational ER translocation. Together, these findings suggest that translating Ty1 mRNA and the genomic RNA of VLPs originate in a single pool and moreover, that co-translational localization of Ty1 RNA nucleates the presumptive VLP assembly site. The separation of nascent Gag from its RNA template by transit through the ER allows Gag to bind translating Ty1 RNA without displaying a cis-preference for its encoding RNA. Retrotransposons are mobile elements that have invaded the genomes of organisms from bacteria to humans. Facilitated by host co-factors, retrotransposon proteins copy their RNA genomes into DNA that integrates into the host genome, causing mutations and genome instability. The yeast Ty1 element belongs to a family of retrotransposons that are related to infectious retroviruses. Ty1 RNA and its coat protein, Gag, assemble into virus-like particles, wherein the RNA is copied into DNA. It was not previously known how Ty1 RNA and Gag are concentrated in a specific cellular location to initiate the assembly of virus-like particles. In this study, we show that Ty1 RNA is brought to the presumptive assembly site during translation by the protein chaperone, signal recognition particle. As Ty1 RNA is translated, the nascent Gag polypeptide enters the lumen of the endoplasmic reticulum, where Gag adopts a stable conformation before returning to the cytoplasm to bind to translating Ty1 RNA. An interaction between Gag molecules bound to translating Ty1 RNA results in the nucleation of the virus-like particle assembly site. Our findings identify new host co-factors in retrotransposon mobility and suggest potential approaches to controlling retrotransposon-associated genome instability in aging and cancer.
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影响因子：
7.8
作者：
Buchan, J. Ross;Muhlrad, Denise;Parker, Roy
通讯作者：
Parker, Roy
DOI：
10.1073/pnas.88.3.936
发表时间：
1991-02-01
影响因子：
11.1
作者：
CURCIO, MJ;GARFINKEL, DJ
通讯作者：
GARFINKEL, DJ
影响因子：
5.4
作者：
Fehrmann, F;Jung, M;Kräusslich, HG
通讯作者：
Kräusslich, HG
影响因子：
5.4
作者：
Campbell, S;Oshima, M;Rein, A
通讯作者：
Rein, A
影响因子：
5.6
作者：
Al-Khayat, HA;Bhella, D;Saibil, HR
通讯作者：
Saibil, HR