What is a Checkpoint?
Although the dependencies among cell cycle events and the coordination of growth and division have been recognized for a long time, it was not until Hartwell and Weinert (1989) introduced the concept of ‘checkpoints’ that the underlying regulatory principles became clear. Hartwell and Weinert hypothesized the existence of ‘checkpoint pathways’ by which an uncompleted cell cycle event sends an inhibitory signal to later events.
They provided evidence for such pathways by studying radiation-sensitive mutants
of budding yeast. In response to DNA damage caused by radiation, wild-type cells stop dividing until the damage can be repaired.