sentences:  In addition to its role in activating the DNA damage checkpoint, ATR is thought to function in unperturbed DNA replication.ATR is related to a second checkpoint-activating kinase, ATM, which is activated by double strand breaks in DNA or chromatin disruption.Mutations in ATR are responsible for Seckel syndrome, a rare human disorder that shares some characteristics with ataxia telangiectasia, which results from ATM mutation.