尿嘧啶过载触发全局基因组不稳定并揭示 dUTPdysgenesis 机制
Uracil overload triggers global genome instability and dUTPdysgenesis
在 DUT1 表达减弱的 Saccharomyces cerevisiae 中，尿嘧啶过载会引发点突变、重组与非整倍性等全局基因组改变，删除 UNG1 可抑制大部分诱导突变和杂合性缺失（LOH），表明碱基切除修复是这些基因组变异的主要驱动因素，而非整倍性直接依赖完整基因组尿嘧啶的持续存在。机制上，大量尿嘧啶损伤通过耗竭 Ung1 和 Apn1 造成修复瓶颈，使突变主要发生在非同胸腺嘧啶位点；持续存在的静态 AP 位点优先激活产生间质型 LOH 的同源重组亚通路，而 Apn1 介导的加工则将重组导向末端型 LOH。
来源：Nucleic Acids Research · doi.org
Uracil accumulation in DNA is a pervasive threat to genomic integrity, yet the global dynamics of how uracil overload drives genome instability remain elusive. Using Saccharomyces cerevisiae strains with attenuated dUTPase (DUT1) expression, we mapped the landscapes of genomic alterations including point mutations, recombination, and aneuploidy. Deletion of the UNG1 suppressed most induced mutations and loss-of-heterozygosity (LOH), identifying base excision repair as the primary driver of genomic alterations, whereas aneuploidy directly depends on the persistence of intact genomic uracil. Mechanistically, beyond localized bypass of static AP sites by translesion synthesis polymerases, the massive influx of uracil lesions induces a repair bottleneck by depleting Ung1 and Apn1. This resource titration, coupled with downstream processing intermediates, primarily drives mutagenesis at heterologous nonthymine positions. Furthermore, persistent static AP sites preferentially stimulate homologous recombination sub-pathway that yield interstitial LOH, whereas Apn1-mediated processing channels recombination toward terminal LOH. Crucially, we define a novel post-zygotic isolation mechanism, dUTPdysgenesis, where parental wild-type Ung1 unleashes an immediate enzymatic shock against a uracil-preloaded genome upon mating, triggering G1-phase chromosomal shattering and mutations. Collectively, this study transitions the paradigm of uracil mutagenesis from localized errors to a global engine of genome instability, bridging nucleotide metabolism, DNA repair kinetics, and speciation barriers.