Slx5/8 alleviates replication stress by promoting mitotic progression

MCM-10 vs. wild type yeast differential analysis using label-free relative quantification and directed mass spectometry using RIPPER. Loss of Mcm10 causes replication stress. We uncovered that S. cerevisiae mcm10-1 mutants rely on the SUMO-targeted E3 ubiquitin ligase complex Slx5/8 and SUMO network for survival. How Slx5/8 suppresses replication stress has remained elusive. We developed a novel intensity-based label-free quantitative mass spectrometry approach and identified SUMO conjugates that were either enriched or depleted in mcm10-1 cells. We reasoned that sumoylated proteins that were decreased in mcm10-1 cells were potential Slx5/8 targets. Such candidates included subunits of the chromosome passenger complex (CPC), Bir1 and Sli15, which we verified to be substrates of the Slx5/8 pathway. CPC is known to positively regulate the spindle assembly checkpoint (SAC), and we show here that the ablation of CPC components and other SAC proteins supports growth of mcm10-1 cells by relieving mitotic arrest. Together, our data provide mechanistic insight into how SUMO and Slx5/8 orchestrate the replication stress response to promote cell survival.