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Autoselection of cytoplasmic yeast virus like elements encoding toxin/antitoxin systems involves a nuclear barrier
Alene Kast1, Raphael Voges1, Michael Schroth2
1Institut für Molekulare Mikrobiologie und Biotechnologie, Westfälische Wilhelms-Universität Münster, Münster, Germany.
Plos Genetics
|May 15, 2015
Summary
High A/T content in yeast virus-like elements (VLEs) prevents nuclear expression of immunity genes. Gene synthesis to lower A/T content enabled functional immunity against anticodon nuclease (ACNase) toxins.
Area of Science:
- Yeast genetics
- Molecular biology
- Virology
Background:
- Cytoplasmic virus-like elements (VLEs) in yeasts like Kluyveromyces lactis possess high A/T content (>75%).
- These VLEs encode toxic anticodon nucleases (ACNases) and cognate immunity proteins.
Purpose of the Study:
- To investigate the functional expression of VLE immunity genes in the nucleus.
- To determine the role of high A/T content in VLE gene regulation and autoselection.
Main Methods:
- Nuclear expression of VLE immunity genes (PaORF4, KlORF3, DrORF5) and assessment of transcript integrity.
- Rapid amplification of 3' ends (RACE) and linker ligation to analyze transcript polyadenylation and fragmentation.
- Gene synthesis to reduce A/T content of immunity genes and evaluate functional expression and immunity.
Main Results:
- Nuclear expression of native immunity genes resulted in transcript fragmentation and failed to confer immunity.
- Polyadenylation and fragmentation of immunity transcripts were observed, linked to ORF-internal poly(A) site cleavage due to high A/T content.
- Reducing A/T content via gene synthesis prevented transcript cleavage, enabling functional nuclear expression and full immunity against cognate ACNases.
Conclusions:
- High A/T content in VLEs acts as a regulatory mechanism to prevent functional nuclear expression of immunity genes.
- This A/T-rich sequence likely prevents the nuclear recruitment of VLE-encoded genes, particularly those involved in autoselection via toxin/antitoxin systems.
- Immunity proteins exhibit specific adaptation to cognate ACNases, with no cross-immunity observed.
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