Saccharomyces cerevisiae Rad9 Acts as a Mec1 Adaptor to Allow Rad53 Activation
Background: The DNA damage checkpoint is a protein kinase-based signaling system that detects and signals physical alterations in DNA. Despite having identified many components of this signaling cascade, the exact mechanisms by which checkpoint kinases are activated after DNA damage, as well as the...
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Published in | Current biology Vol. 15; no. 15; pp. 1364 - 1375 |
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Main Authors | , , , , , |
Format | Journal Article |
Language | English |
Published |
England
Elsevier Inc
09.08.2005
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Subjects | |
Online Access | Get full text |
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Summary: | Background: The DNA damage checkpoint is a protein kinase-based signaling system that detects and signals physical alterations in DNA. Despite having identified many components of this signaling cascade, the exact mechanisms by which checkpoint kinases are activated after DNA damage, as well as the role of the checkpoint mediators, remain poorly understood.
Results: To elucidate the mechanisms that underlie the
MEC1 and
RAD9-dependent activation of Rad53, the
Saccharomyces cerevisiae ortholog of Chk2, we mapped and characterized in vivo phosphorylation sites present on Rad53 after DNA damage by mass spectrometry. We find that Rad53 requires for its activation multisite phosphorylation on a number of typical and atypical Mec1 phosphorylation sites, thus confirming that Rad53 is a direct target of Mec1, the mammalian ATR homolog. Moreover, by using biochemical reconstitution experiments, we demonstrate that efficient and direct phosphorylation of Rad53 by Mec1 is only observed in the presence of purified Rad9, the archetypal checkpoint mediator. We find that the stimulatory activity of Rad9 requires a phospho- and FHA-dependent interaction with Rad53, which allows Rad53 to be recognized as a substrate for Mec1.
Conclusions: Our results indicate that Rad9 acts as a bona fide signaling adaptor that enables Rad53 phosphorylation by Mec1. Given the high degree of conservation of checkpoint signaling in eukaryotes, we propose that one of the critical functions of checkpoint mediators such as MDC1, 53BP1, or Brca1 is to act as PIKK adaptors during the DNA damage response. |
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Bibliography: | ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-3 content type line 23 ObjectType-Review-1 ObjectType-Article-1 ObjectType-Feature-2 |
ISSN: | 0960-9822 1879-0445 |
DOI: | 10.1016/j.cub.2005.06.063 |