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Molecular and Cellular Biology, February 2004, p. 1292-1300, Vol. 24, No. 3
0270-7306/04/$08.00+0     DOI: 10.1128/MCB.24.3.1292-1300.2003
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Quaternary Structure of ATR and Effects of ATRIP and Replication Protein A on Its DNA Binding and Kinase Activities

Keziban Ünsal-Kaçmaz and Aziz Sancar*

Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599

Received 5 October 2003/ Returned for modification 5 November 2003/ Accepted 6 November 2003

ATR is an essential protein that functions as a damage sensor and a proximal kinase in the DNA damage checkpoint response in mammalian cells. It is a member of the phosphoinositide 3-kinase-like kinase (PIKK) family, which includes ATM, ATR, and DNA-dependent protein kinase. Recently, it was found that ATM is an oligomeric protein that is converted to an active monomeric form by phosphorylation in trans upon DNA damage, and this raised the possibility that other members of the PIKK family may be regulated in a similar manner. Here we show that ATR is a monomeric protein associated with a smaller protein called ATRIP with moderate affinity. The ATR protein by itself or in the form of the ATR-ATRIP heterodimer binds to naked or replication protein A (RPA)-covered DNAs with comparable affinities. However, the phosphorylation of RPA by ATR is dependent on single-stranded DNA and is stimulated by ATRIP. These findings suggest that the regulation and mechanism of action of ATR are fundamentally different from those of the other PIKK proteins.


* Corresponding author. Mailing address: Department of Biochemistry and Biophysics, Mary Ellen Jones Building CB7260, University of North Carolina School of Medicine, Chapel Hill, NC 27599. Phone: (919) 962-0115. Fax: (919) 843-8627. E-mail: Aziz_Sancar{at}med.unc.edu


Molecular and Cellular Biology, February 2004, p. 1292-1300, Vol. 24, No. 3
0022-538X/04/$08.00+0     DOI: 10.1128/MCB.24.3.1292-1300.2003
Copyright © 2004, American Society for Microbiology. All Rights Reserved.




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