Ataxia telangiectasia mutated (ATM)- and Rad3-related protein (ATR) is a 
phosphatidylinositol-kinase (PIK)-related kinase that has been implicated in the 
response of human cells to multiple forms of DNA damage and may play a role in 
the DNA replication checkpoint. The purification of an ATR complex allowed 
identification of chromodomain-helicase-DNA-binding protein 4 (CHD4) as an 
ATR-associated protein by tandem mass spectrometric sequencing. CHD4 (also 
called Mi-2beta) is a component of a histone-deacetylase-2 (HDAC2)-containing 
complex, the nucleosome remodeling and deacetylating (NRD) complex. Endogenous 
ATR, CHD4, and HDAC2 are shown to coimmunoprecipitate, and ATR and HDAC2 coelute 
through two biochemical purification steps. Other members of the NRD complex, 
HDAC1, MTA1, and MTA2, are also detectable in ATR immunoprecipitates. ATR's 
association with CHD4 and HDAC2 suggests that there may be a linkage between 
ATR's role in mediating checkpoints induced by DNA damage and chromatin 
modulation via remodeling and deacetylation.