Rad53/Chk2 couples mitochondrial outputs and ROS with G2/M cell cycle progression
Cell-cycle progression requires coordination with cellular metabolism, yet how checkpoint kinases contribute to this coordination during normal growth remains poorly understood. Here, we uncover an unexpected role for the checkpoint kinase Rad53/Chk2 in coupling mitochondrial and redox homeostasis to G2/M progression. In prototrophic S. cerevisiae, Rad53 loss (rad53{Delta}) disrupts cell-cycle progression and causes cells to accumulate in G2/M, alongside extensive metabolic remodelling with increased tricarboxylic acid (TCA) cycle flux. Mitochondrial proteomics reveals altered relative abundances of individual electron transport chain proteins, and mitochondrial membrane potential increases without increased oxygen consumption or ATP generation. This altered mitochondrial state is associated with elevated reactive oxygen species (ROS) and oxidative stress. Genetic analyses establish that mitochondrial phenotypes require Rad53 kinase activity and are distinct from the loss of SML1. Antioxidant treatment rescues cell-division, budding defects and the accumulation of abnormally sized cells, establishing ROS as a primary cause of cell-cycle defects. Thus, Rad53 couples mitochondrial and redox homeostasis to G2/M progression during normal growth.