<b>Structural determinants within the subunit protein of Ty1 virus‐like particles</b>

Martin‐Rendon, Enca; Marfany, Gemma; Wilson, Stuart M.; Ferguson, David; Kingsman, Susan M.; Kingsman, Alan J.

doi:10.1046/j.1365-2958.1996.d01-1716.x

Cited by 19 publications

(27 citation statements)

References 27 publications

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“…Whether p22 enters the ER remains to be determined. Ty1 GAG mutations that confer a trans-dominant negative phenotype (80)(81)(82) or affect VLP assembly (83) have been isolated, and some of these mutations map in p22. A synthetic peptide containing sequences within p22 also displays RNA chaperone activity (84), which is required for specific RNA transactions during the retroviral life cycle such as virion assembly, RNA packaging, primer annealing, and reverse transcription (85).…”

Section: Discussionmentioning

confidence: 99%

A trans -Dominant Form of Gag Restricts Ty1 Retrotransposition and Mediates Copy Number Control

Saha

Mitchell

Nishida

et al. 2015

J Virol

232

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Saccharomyces cerevisiae and Saccharomyces paradoxus lack the conserved RNA interference pathway and utilize a novel form of copy number control (CNC) to inhibit Ty1 retrotransposition. Although noncoding transcripts have been implicated in CNC, here we present evidence that a truncated form of the Gag capsid protein (p22) or its processed form (p18) is necessary and sufficient for CNC and likely encoded by Ty1 internal transcripts. Coexpression of p22/p18 and Ty1 decreases mobility more than 30,000-fold. p22/p18 cofractionates with Ty1 virus-like particles (VLPs) and affects VLP yield, protein composition, and morphology. Although p22/p18 and Gag colocalize in the cytoplasm, p22/p18 disrupts sites used for VLP assembly. Glutathione Stransferase (GST) affinity pulldowns also suggest that p18 and Gag interact. Therefore, this intrinsic Gag-like restriction factor confers CNC by interfering with VLP assembly and function and expands the strategies used to limit retroelement propagation. IMPORTANCERetrotransposons dominate the chromosomal landscape in many eukaryotes, can cause mutations by insertion or genome rearrangement, and are evolutionarily related to retroviruses such as HIV. Thus, understanding factors that limit transposition and retroviral replication is fundamentally important. The present work describes a retrotransposon-encoded restriction protein derived from the capsid gene of the yeast Ty1 element that disrupts virus-like particle assembly in a dose-dependent manner. This form of copy number control acts as a molecular rheostat, allowing high levels of retrotransposition when few Ty1 elements are present and inhibiting transposition as copy number increases. Thus, yeast and Ty1 have coevolved a form of copy number control that is beneficial to both "host and parasite." To our knowledge, this is the first Gag-like retrotransposon restriction factor described in the literature and expands the ways in which restriction proteins modulate retroelement replication.

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Section: Discussionmentioning

confidence: 99%

A trans -Dominant Form of Gag Restricts Ty1 Retrotransposition and Mediates Copy Number Control

Saha

Mitchell

Nishida

et al. 2015

J Virol

232

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“…This region is predicted to form an alpha-helical domain, which could promote recognition by SRP [52], [53]. Interestingly, amino acids 341 through 346 (LDIHAI) have been shown to be critical for the formation of VLPs [54], [55].…”

Section: Discussionmentioning

confidence: 99%

Co-translational Localization of an LTR-Retrotransposon RNA to the Endoplasmic Reticulum Nucleates Virus-Like Particle Assembly Sites

2014

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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.

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“…Gag is the only Ty1 protein domain necessary for the formation of VLPs, which assemble even when Gag is expressed in E. coli [106,107]. The smallest fragments of the 440 amino acid-Gag protein that can assemble into particles span amino acids 41-346 or 31-363 [107-109]. Within this minimal Gag fragment, several regions have been shown to be important in assembly, including amino acids 41 to 62, 114 to 147, 223 to 287 and 330 to 346 (reviewed in [110]).…”

Section: Post-translational Steps In Retrotranspositionmentioning

confidence: 99%

“…Within this minimal Gag fragment, several regions have been shown to be important in assembly, including amino acids 41 to 62, 114 to 147, 223 to 287 and 330 to 346 (reviewed in [110]). Remarkably, one or two amino acid substitutions can completely block assembly or increase the size of VLPs as much as 8-fold [109]. The N-terminus of Gag is on the surface of the VLP, while the C-terminus of both mature and immature forms of Gag is buried in the core [108].…”

Section: Post-translational Steps In Retrotranspositionmentioning

confidence: 99%

The Ty1 LTR-Retrotransposon of Budding Yeast,Saccharomyces cerevisiae

2015

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Summary Long-terminal repeat (LTR)-retrotransposons generate a copy of their DNA (cDNA) by reverse transcription of their RNA genome in cytoplasmic nucleocapsids. They are widespread in the eukaryotic kingdom and are the evolutionary progenitors of retroviruses [1]. The Ty1 element of the budding yeast Saccharomyces cerevisiae was the first LTR-retrotransposon demonstrated to mobilize through an RNA intermediate, and not surprisingly, is the best studied. The depth of our knowledge of Ty1 biology stems not only from the predominance of active Ty1 elements in the S. cerevisiae genome but also the ease and breadth of genomic, biochemical and cell biology approaches available to study cellular processes in yeast. This review describes the basic structure of Ty1 and its gene products, the replication cycle, the rapidly expanding compendium of host co-factors known to influence retrotransposition and the nature of Ty1's elaborate symbiosis with its host. Our goal is to illuminate the value of Ty1 as a paradigm to explore the biology of LTR-retrotransposons in multicellular organisms, where the low frequency of retrotransposition events presents a formidable barrier to investigations of retrotransposon biology.

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Structural determinants within the subunit protein of Ty1 virus‐like particles

Cited by 19 publications

References 27 publications

A trans -Dominant Form of Gag Restricts Ty1 Retrotransposition and Mediates Copy Number Control

A trans -Dominant Form of Gag Restricts Ty1 Retrotransposition and Mediates Copy Number Control

Co-translational Localization of an LTR-Retrotransposon RNA to the Endoplasmic Reticulum Nucleates Virus-Like Particle Assembly Sites

The Ty1 LTR-Retrotransposon of Budding Yeast,Saccharomyces cerevisiae

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