# sic1 mutation leads to rDNA instability by partial duplication with SIR4

## TL;DR

A mutation in the sic1 gene causes instability in the ribosomal DNA and chromosome IV in yeast through increased SIR4 gene dosage.

## Contribution

This study reveals a novel link between rDNA instability and chromosome IV duplication via SIR4 gene dosage increase.

## Key findings

- The sic1 mutation causes instability in both rDNA and chromosome IV.
- Partial duplication of chromosome IV increases SIR4 gene dosage, leading to rDNA instability.
- Ty element-mediated recombination contributes to chromosome IV elongation.

## Abstract

The ribosomal RNA gene cluster (rDNA) in Saccharomyces cerevisiae consists of about 150 tandem copies, making it a fragile site prone to copy number changes through recombination among the repeat. While extensive research has been conducted to understand the mechanisms for rDNA stability maintenance, the relationship between the stability maintenance of rDNA and other genomic regions remains unclear. In this study, we identified a mutant, sic1, that exhibited instability in both rDNA and chromosome IV (chr.IV). We revealed that Ty element-mediated ectopic recombination leads to partial duplication and elongation of chr.IV. Furthermore, we found that rDNA instability is caused by an increased SIR4 gene dosage resulting from this partial duplication. These findings suggest a link between the stability of rDNA and other genomic regions.

Graphical Abstract