MET18 deficiency leads to elevated single-stranded DNA at the replication fork and destabilizes the yeast genome

Iron-sulfur (Fe-S) clusters often act as protein cofactors, and many enzymes involved in DNA replication and repair require them for proper function. However, the precise mechanisms by which Fe-S clusters influence enzyme activity remain incompletely understood. It has been shown previously that a mutation in the MET18 gene, encoding a key component of the cytosolic Fe-S cluster assembly machinery, elevates the rate of mutations in haploid Saccharomyces cerevisiae cells. In the current study, we demonstrate that in diploid yeast cells, the met18 mutation results in an elevation in loss-of-heterozygosity (LOH) events and large interstitial chromosomal deletions and duplications. We also found 46-fold and 55-fold increases in terminal deletions and duplications, respectively. By expressing the human APOBEC3B gene in yeast, we show that the rate of CG to TA mutations increased threefold in the met18 strain, and these mutations were enriched four-fold on the lagging-strand template relative to the leading-strand template, indicating the presence of elevated levels of single-stranded DNA (ssDNA) at replication forks. Overall, this study shows that loss of MET18 causes extensive genome instability in yeast, providing additional insights into how Fe-S clusters regulate genome stability.