FunctionSerine/threonine protein kinase which activates checkpoint signaling upon genotoxic stresses such as ionizing radiation (IR), ultraviolet light (UV), or DNA replication stalling, thereby acting as a DNA damage sensor. RUniProtKB:Q9JKK8, PubMed:10597277, PubMed:10608806, PubMed:10859164, PubMed:11114888, PubMed:11418864, PubMed:11673449, PubMed:11721054, PubMed:11865061, PubMed:12526805, PubMed:12791985, PubMed:12814551, PubMed:14657349, PubMed:14729973, PubMed:14742437, PubMed:15210935, PubMed:15314022, PubMed:15496423, PubMed:16260606, PubMed:21144835, PubMed:27723717, PubMed:27723720, PubMed:33848395, PubMed:9427750, PubMed:9636169, PubMed:9925639}.