Srs2 and Sgs1 DNA helicases associate with Mre11 in different sub-complexes following checkpoint activation and CDK1-mediated Srs2 phosphorylation.
Irene Chiolo (1), Walter Carotenuto (1), Giulio Maffioletti (2), John H.J. Petrini (3), Marco Foiani (1), Giordano Liberi (1)
(1) FIRC Institute of Molecular On, IFOM, Via Adamello, 16, Milano, 20139, Italy; (2) The University of Dundee, Dow Street, Dundee, DD1 5EH, UK; (3) Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY, 10021, USA
Mutations in the genes encoding the BLM and WRN RecQ DNA helicases and the MRE11-RAD50-NBS1 complex lead to genome instability and cancer predisposition syndromes. The yeast Sgs1 RecQ helicase and the Mre11 protein, together with the Srs2 DNA helicase, prevent chromosome rearrangements and are implicated in the DNA damage checkpoint response and in DNA recombination. By searching for Srs2 physical interactors, we have identified Sgs1 and Mre11. We show that Srs2, Sgs1 and Mre11 form a large size complex likely together with yet unidentified proteins. This complex reorganizes into Srs2-Mre11 and Sgs1-Mre11 sub-complexes following DNA damage-induced activation of the Mec1 and Tel1 checkpoint kinases. The defects in sub-complex formation observed in mec1 and tel1 cells can be recapitulated in srs2-7AV mutants that are hypersensitive to intra-S DNA damage and are altered in the DNA damage-induced and Cdk1-dependent phosphorylation of Srs2. Altogether our observations indicate that Mec1 and Tel1-dependent checkpoint pathways modulate the functional interactions between Srs2, Sgs1 and Mre11 and that the Srs2 DNA helicase represents an important target of the Cdk1-mediated cellular response induced by DNA damage.