RNA polymerase I mutant affects ribosomal RNA processing and ribosomal DNA stability.
Christophe Normand1, Christophe Dez1, Lise Dauban1
1Molecular, Cellular and Developmental Biology Unit (MCD), Centre de Biologie Integrative (CBI), University of Toulouse, CNRS, UPS, Toulouse, France.
RNA Biology
|July 25, 2024
Summary
A novel mutant RNA polymerase I (RNAPI) in yeast causes ribosomal RNA (rRNA) processing defects and genomic instability at the ribosomal DNA (rDNA) locus. This instability leads to cell death, highlighting the importance of proper rRNA processing for genome stability.
Area of Science:
- Molecular Biology
- Genetics
- Yeast Genetics
Background:
- Transcription is a key driver of genomic instability.
- The ribosomal RNA (rDNA) locus, composed of repetitive genes, is highly transcribed by RNA polymerase I (RNAPI).
- Proper processing and assembly of nascent rRNA are crucial for cellular function.
Purpose of the Study:
- To investigate the consequences of a specific mutant RNAPI (CARA-RNAPI) in *Saccharomyces cerevisiae*.
- To determine the role of CARA-RNAPI in rRNA processing and rDNA genomic stability.
- To elucidate the link between aberrant rRNA processing and rDNA instability.
Main Methods:
- Characterization of CARA-RNAPI mutant yeast.
- Analysis of rRNA processing intermediates and accumulation.
- Assessment of rDNA genomic instability, including copy number variation.
- Synthetic lethality assays with mutants affecting rDNA condensation (monopolin mutants).
- Investigation of interactions with the exosome complex.
Main Results:
- CARA-RNAPI causes a novel rRNA processing defect, leading to the accumulation of unprocessed 35S rRNA.
- rRNA accumulation is exacerbated in mutants with impaired exosome function.
- CARA-RNAPI exhibits synthetic lethality with monopolin mutants, indicating an impact on rDNA organization.
- CARA-RNAPI increases rDNA copy number variation, a phenotype suppressed by reduced rDNA copy number.
- The observed lethality is linked to chromosome segregation defects arising from rDNA instability.
Conclusions:
- Constitutive association of Rrn3 with transcribing RNAPI leads to rRNA processing defects.
- Accumulation of unprocessed rRNAs disrupts rDNA organization and compromises rDNA stability.
- Aberrant rRNA processing is a significant contributor to genomic instability at the rDNA locus.
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