Abstract
Long-terminal repeat (LTR) retrotransposons are transposable genetic elements that replicate intracellularly, and can be considered progenitors of retroviruses. Ty1 and Ty3 are the most extensively characterized LTR retrotransposons whose RNA genomes provide the template for both protein translation and genomic RNA that is packaged into virus-like particles (VLPs) and reverse transcribed. Genomic RNAs are not divided into separate pools of translated and packaged RNAs, therefore their trafficking and packaging into VLPs requires an equilibrium between competing events. In this review, we focus on Ty1 and Ty3 genomic RNA trafficking and packaging as essential steps of retrotransposon propagation. We summarize the existing knowledge on genomic RNA sequences and structures essential to these processes, the role of Gag proteins in repression of genomic RNA translation, delivery to VLP assembly sites, and encapsidation.
Highlights
Long-terminal repeat (LTR) retrotransposons are transposable genetic elements that comprise a significant fraction of many eukaryotic genomes [1,2]
Ty1 pseudoknot in RNA encapsidation could not be demonstrated [68]. Both genetic studies and limited in vitro data imply that Ty encapsidation relies on recognition of cis-acting sequences in genomic RNA (gRNA) by Gag. It is not known if the same nucleotide sequences are recognized by Gag during nuclear export, trafficking to retrosomes and gRNA packaging [28,42,60]
Packaged RNA, their trafficking and packaging into virus-like particles (VLPs) requires an equilibrium between competing events of translation and packaging
Summary
Long-terminal repeat (LTR) retrotransposons are transposable genetic elements that comprise a significant fraction of many eukaryotic genomes [1,2]. They are progenitors of retroviruses, differing in that they replicate intracellularly [3,4,5]. LTR-retrotransposons replicate via an RNA intermediate and insert their double-stranded DNA into the host genome [6,7,8]. Full-length Ty1 or Ty3 genomic RNA (gRNA) plays dual role in replication and serves as a template for translation [19] as well as the retrotransposon genome that is packaged into virus like particles (VLP) and reverse transcribed [6,8]. A fine balance between gRNA translation and packaging events is required for productive retrotransposition
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