title: ATRMec1 phosphorylation-independent activation of Chk1 in vivo.
abstract: The conserved protein kinase Chk1 is a player in the defense against DNA damage and replication blocks. The current model is that after DNA damage or replication blocks, ATR(Mec1) phosphorylates Chk1 on the non-catalytic C-terminal domain. However, the mechanism of activation of Chk1 and the function of the Chk1 C terminus in vivo remains largely unknown. In this study we used an in vivo assay to examine the role of the C terminus of Chk1 in the response to DNA damage and replication blocks. The conserved ATR(Mec1) phosphorylation sites were essential for the checkpoint response to DNA damage and replication blocks in vivo; that is, that mutation of the sites caused lethality when DNA replication was stalled by hydroxyurea. Despite this, loss of the ATR(Mec1) phosphorylation sites did not change the kinase activity of Chk1 in vitro. Furthermore, a single amino acid substitution at an invariant leucine in a conserved domain of the non-catalytic C terminus restored viability to cells expressing the ATR(Mec1) phosphorylation site-mutated protein and relieved the requirement of an upstream mediator for Chk1 activation. Our findings show that a single amino acid substitution in the C terminus, which could lead to an allosteric change in Chk1, allows it to bypass the requirement of the conserved ATR(Mec1) phosphorylation sites for checkpoint function.
authors.affiliation: Department of Pharmacology and Toxicology, Norris Cotton Cancer Center, Dartmouth Medical School, Hanover, New Hampshire 03755 and Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0524.
authors.forename: Yinhuai
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Department of Pharmacology and Toxicology, Norris Cotton Cancer Center, Dartmouth Medical School, Hanover, New Hampshire 03755 and Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0524.
authors.forename: Julie M
authors.initials: JM
authors.lastname: Caldwell
authors.affiliation: Department of Pharmacology and Toxicology, Norris Cotton Cancer Center, Dartmouth Medical School, Hanover, New Hampshire 03755 and Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0524.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Pereira
authors.affiliation: Department of Pharmacology and Toxicology, Norris Cotton Cancer Center, Dartmouth Medical School, Hanover, New Hampshire 03755 and Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0524.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Baker
authors.affiliation: Department of Pharmacology and Toxicology, Norris Cotton Cancer Center, Dartmouth Medical School, Hanover, New Hampshire 03755 and Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0524. Electronic address: Yolanda.Sanchez@Dartmouth.edu.
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Sanchez
mesh_terms: D019943:Amino Acid Substitution; D000071877:Checkpoint Kinase 1; D004249:DNA Damage / Q000187:drug effects / Q000502:physiology*; D004261:DNA Replication / Q000187:drug effects / Q000502:physiology*; D004789:Enzyme Activation / Q000502:physiology; D006918:Hydroxyurea / Q000494:pharmacology; D048369:MAP Kinase Kinase 1 / Q000235:genetics / Q000378:metabolism*; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D017354:Point Mutation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D019384:Nucleic Acid Synthesis Inhibitors; D029701:Saccharomyces cerevisiae Proteins; D011494:Protein Kinases; D000071877:Checkpoint Kinase 1; D048369:MAP Kinase Kinase 1; D006918:Hydroxyurea