The Rad9-Hus1-Rad1 (9-1-1) clamp activates checkpoint signaling via TopBP1.
DNA replication stress triggers the activation of Checkpoint Kinase 1 (Chk1) in a pathway that requires the independent chromatin loading of the ATRIP-ATR (ATR-interacting protein/ATM [ataxia-telangiectasia mutated]-Rad3-related kinase) complex and the Rad9-Hus1-Rad1 (9-1-1) clamp. We show that Rad9's role in Chk1 activation is to bind TopBP1, which stimulates ATR-mediated Chk1 phosphorylation via TopBP1's activation domain (AD), a domain that binds and activates ATR. Notably, fusion of the AD to proliferating cell nuclear antigen (PCNA) or histone H2B bypasses the requirement for the 9-1-1 clamp, indicating that the 9-1-1 clamp's primary role in activating Chk1 is to localize the AD to a stalled replication fork.
Delacroix
Sinny
S
Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA.
Wagner
Jill M
JM
Kobayashi
Masahiko
M
Yamamoto
Ken-ichi
K
Karnitz
Larry M
LM
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D000071877:Checkpoint Kinase 1; D002645:Chickens; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005092:Exonucleases / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008954:Models, Biological; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C549605:HUS1 protein, human; C462949:HUS1B protein, human; D009687:Nuclear Proteins; C113575:Rad17 protein, human; C110513:TOPBP1 protein, human; C069930:rad9 protein; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D005092:Exonucleases; C113574:Rad1 protein, human