Sauty Safia Mahabub, Fisher Ashley, Dolson Andrew, Yankulov Krassimir
Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G2W1, Canada.
J Cell Sci. 2024 Dec 15;137(24). doi: 10.1242/jcs.262006. Epub 2024 Dec 17.
The FLO genes in Saccharomyces cerevisiae are repressed by heterochromatin formation, involving histone deacetylases, transcription factors and non-coding RNAs. Here, we report that mutations in the processivity factor POL30 (PCNA) that show transient derepression at the subtelomeres and the mating-type loci do not derepress FLO loci. However, deletions of the replisome stability factors RRM3 and TOF1 along with pol30 mutations induced flocculation phenotypes. The phenotypes correlated with increased expression of reporter proteins driven by the FLO11 promoter, the frequency of silent to active conversions of FLO11, and reduced expression of the regulatory long non-coding RNAs ICR1 and PWR1. Alterations in the local replication landscape of FLO11 indicate a link between defects in the fork protection complex and the stability of gene silencing. Analyses of these mutants at the subtelomeres and the HMLα locus showed a similar derepression phenotype and suggest transient instability of both active and silent states of FLO11. We conclude that RRM3 and TOF1 interact differentially with the pol30 mutations to promote transient derepression or complete epigenetic conversions of FLO11. We suggest that the interaction between POL30, RRM3 and TOF1 is essential to maintain epigenetic stability at the studied loci.
酿酒酵母中的FLO基因会被异染色质形成所抑制，这一过程涉及组蛋白去乙酰化酶、转录因子和非编码RNA。在此，我们报告称，在端粒和交配型位点表现出瞬时去抑制的持续性因子POL30（增殖细胞核抗原）突变并不会使FLO位点去抑制。然而，复制体稳定性因子RRM3和TOF1的缺失以及pol30突变会诱导絮凝表型。这些表型与由FLO11启动子驱动的报告蛋白表达增加、FLO11从沉默到活跃转换的频率以及调控性长链非编码RNA ICR1和PWR1的表达降低相关。FLO11局部复制格局的改变表明叉保护复合体缺陷与基因沉默稳定性之间存在联系。对这些突变体在端粒和HMLα位点的分析显示出类似的去抑制表型，并表明FLO11的活跃和沉默状态均存在瞬时不稳定性。我们得出结论，RRM3和TOF1与pol30突变的相互作用方式不同，以促进FLO11的瞬时去抑制或完全表观遗传转换。我们认为，POL30、RRM3和TOF1之间的相互作用对于在所研究位点维持表观遗传稳定性至关重要。
