Ataxia Telangiectasia Mutated (ATM) and Rad 3-related protein (ATR) is a phosphatidylinositol kinase (PK)-related kinase which functions in response to DNA damage and repair as well as at DNA replication checkpoints during the cell cycle. ATR is a member of the DNA-PK kinases closely related to ATM and DNA-PK for which DNA stimulates the observed kinase activity. Chromosomal remodeling proteins have also been reported to associate with ATR complexes. Several known components of the NuRD complex including histone deacetylase 1 (HDAC1), HDAC2, and CHD4.Synonyms: Ataxia telangiectasia and Rad3-related protein, FRAP-related protein 1, Serine/threonine-protein kinase ATR