Novel transcript truncating function of Rap1p revealed by synthetic codon-optimized Ty1 retrotransposon

Area of Science:

• Molecular Biology
• Genetics
• Synthetic Biology

Background:

• Retrotransposons like Ty1 are mobile genetic elements.
• Understanding their regulation is key to controlling their activity and for applications in synthetic biology.

Purpose of the Study:

• To identify and characterize sequences that down-regulate retrotransposon activity.
• To explore the mechanism of repression and its potential applications.

Main Methods:

• Extensive mutagenesis and recoding of Ty1 retrotransposon to create a synthetic version (CO-Ty1).
• Mapping of the repressing sequence within the reverse transcriptase (RT) domain.
• Reporter gene assays (GFP) to test non-specific repression.
• Mutagenesis and chromatin immunoprecipitation to identify the mediating factor (Rap1p).
• Analysis of RNAP II occupancy and RNA species.

Main Results:

• CO-Ty1 exhibited defective retrotransposition and reduced Ty1 protein and RNA levels.
• A ~20-bp region in the RT domain was identified as responsible for repression.
• This repressing sequence reduced expression of a heterologous gene (GFP).
• Rap1p was identified as the protein mediating this down-regulation.
• A significant reduction in RNAP II occupancy and production of truncated RNA were observed downstream of the Rap1p binding site.

Conclusions:

• A novel mechanism of transcriptional regulation involving Rap1p acting as a transcriptional roadblock is proposed.
• The identified sequence offers a tool for down-regulating gene expression in various contexts.
• This finding has implications for controlling mobile genetic elements and designing synthetic gene circuits.