Cell Cycle Unraveling Mec3's Role in G₁ and G₂-M

DNA damage can halt or slow progression through the cell cycle allowing time for the cell to repair the damage and thus maintain genomic fidelity. In Saccharomyces cerevisiae, deletion of MEC3, encoding a component of the DNA damage sensor complex, results in loss of activation of the G₁ and G₂ to mitosis (G₂-M) checkpoints. Biochemically, activation of the G₁ and G₂-M checkpoints is associated with activation of kinases, including Mec1, and phosphorylation of Rad53 and Rad9. Phosphorylation of Rad53 does not occur in mec3 cells upon DNA damage in G₁ or G₂. Giannattasio et al. identified a mutant version of Mec3 (mec3-dn) that produces yeast defective in phosphorylation of Rad53 in response to DNA damage in G₁ and activation of only this early checkpoint. The G₂-M checkpoint was still functional and Rad53 was phosphorylated in response to DNA damage in G₂. Rad53 phosphorylation depends on an interaction with phosphorylated Rad9. Using DNA damage sensor complexes isolated from cells expressing mec3-dn, the authors found that phosphorylation of Rad9 and its interaction with Rad53 were defective when the cells were treated to induce DNA damage in G₁, but not when the cells were treated to induce DNA damage in G₂. In mec3-dn cells, deletion of TEL1, encoding a kinase, resulted in loss of the G₂-M checkpoint and Rad53 phsophorylation in response to G₂ DNA damage, uncovering a role for Tel1 in the G₂-M checkpoint. Thus, this new Mec3 mutant has allowed detection of different roles for Mec3 in G₁ and G₂-M checkpoint signaling and of a role for Tel1 in the G₂-M checkpoint to be uncovered.

M. Giannattasio, E. Sommariva, R. Vercillo, F. Lippi-Boncambi, G. Liberi, M. Foiani, P. Plevani, M. Muzi-Falconi, A dominant-negative MEC3 mutant uncovers new functions for the Rad17 complex and Tel1. Proc. Natl. Acad. Sci. U.S.A. 99, 12997-13002 (2002). [Abstract] [Full Text]

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VIRTUAL JOURNAL
A dominant-negative MEC3 mutant uncovers new functions for the Rad17 complex and Tel1

Michele Giannattasio, Elena Sommariva, Raffaella Vercillo, Filippo Lippi-Boncambi, Giordano Liberi, Marco Foiani, Paolo Plevani, and Marco Muzi-Falconi (1 October 2002)
PNAS 99 (20), 12997. [DOI: 10.1073/pnas.202463999]
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