FIGURE 4.

A working model of DNA damage-induced G₂/M checkpoint activation through the Bora-Plk1 pathway. Under normal, unstressed conditions, Bora accumulates in G₂ phase, binds to Plk1, and facilitates Plk1 activation by Aurora A. Plk1 then activates its downstream targets, and cells enter mitosis. However, when genotoxic stressors are present during G₂ phase, ATR is activated and phosphorylates Bora at Thr-501, which is recognized by SCF-β-TRCP and results in Bora degradation. Thus, Plk1 is kept inactivated, and cells are arrested at G₂ phase. Ub, ubiquitination.