Structure-Function Model for Kissing Loop Interactions That Initiate Dimerization of Ty1 RNA

Area of Science:

• Molecular Biology
• Genetics
• RNA Structure

Background:

• The Ty1 retrotransposon genomic RNA is packaged as a dimer into virus-like particles.
• The 5' terminus of Ty1 RNA contains cis-acting sequences essential for translation, packaging, and reverse transcription initiation (TIPIRT).

Purpose of the Study:

• To identify specific RNA motifs within the TIPIRT domain responsible for Ty1 RNA dimerization and packaging.
• To develop an in vitro structural model of the TIPIRT domain using single-nucleotide resolution RNA structural data.

Main Methods:

• In vitro structural analysis of the Ty1 RNA TIPIRT domain.
• Site-directed mutagenesis to disrupt specific RNA structural elements (pseudoknot stems, hairpin motifs).
• Assays to measure retrotransposition efficiency and RNA stability in cis and trans.

Main Results:

• The first 326 nucleotides of Ty1 RNA form a pseudoknot with two stems (S1 and S2) and two structured loops.
• Disrupting pseudoknot stems reduced retrotransposition; mutations in S2 destabilized RNA in cis and trans.
• Two hairpins with complementary motifs nested in the pseudoknot loops were identified; mutations here also reduced retrotransposition and RNA stability.
• Compensatory mutations restored base-pairing and rescued retrotransposition and RNA stability.

Conclusions:

• A model is proposed where a Ty1 RNA kissing complex, involving two intermolecular kissing-loop interactions, initiates RNA dimerization and packaging.
• Specific RNA structural motifs within the TIPIRT domain are critical for Ty1 retrotransposon dimerization, packaging, and replication.
• The pseudoknot structure and associated hairpins play essential roles in maintaining RNA stability and facilitating retrotransposition.