The DNA damage and the DNA synthesis checkpoints converge at the MBF transcription factor

DNA damage is an ongoing threat to both the ability of the cell to faithfully transmit genetic information to its offspring as well as to its own survival. In order to maintain genomic integrity, eukaryotes have developed a highly conserved mechanism to detect, signal and repair damage in DNA, known as the DNA damage response (DDR). In fission yeast the two DDR pathways converge at the regulation of single transcriptional factor complex (MBF) resulting in opposite directions. We have shown that when the DNA-synthesis checkpoint is activated, Max1 is phosphorylated by Cds1 resulting in the abrogation of its binding to MBF. As a consequence, MBF-dependent transcription is maintained active until cells are able to overcome the replication challenge. In contrast, upon DNA damage, Chk1 the effector kinase of DNA damage checkpoint is activated and blocks the cell cycle progression, inducing DNA repair and repressing the MBF dependent transcription. We have revealed that Cdc10 is the target of the DNA-damage checkpoint and when cells are treated with MMS or are exposed to IR, Chk1 phosphorylates Cdc10 inducing the exit of MBF from chromatin. The consequence is that under these conditions, MBF-dependent transcription is repressed. Thus, Max1 and Cdc10 couple normal cell cycle regulation and the DNA-synthesis and DNA-damage checkpoints into MBF

Budding yeast complete DNA synthesis after chromosome segregation begins

To faithfully transmit genetic information, cells must replicate their entire genome before division. This is thought to be ensured by the temporal separation of replication and chromosome segregation. Here we show that in 20-40% of unperturbed yeast cells, DNA synthesis continues during anaphase, late in mitosis. High cyclin-Cdk activity inhibits DNA synthesis in metaphase, and the decrease in cyclin-Cdk activity during mitotic exit allows DNA synthesis to finish at subtelomeric and some difficult-to-replicate regions. DNA synthesis during late mitosis correlates with elevated mutation rates at subtelomeric regions, including copy number variation. Thus, yeast cells temporally overlap DNA synthesis and chromosome segregation during normal growth, possibly allowing cells to maximize population-level growth rate while simultaneously exploring greater genetic space.This study was supported by Ministerio de Economía y Competitividad (MINECO) (BFU2015-68351-P) and AGAUR (2014SGR0974 & 2017SGR1054) grants to L.B.C. and the Unidad de Excelencia María de Maeztu, funded by the MINECO (MDM-2014-0370); the European Research Council (ERC) Starting Grant 2010-St-20091118 to Ma.M., the Spanish Ministry of Economy and Competitiveness, ‘Centro de Excelencia Severo Ochoa 2013–2017’, SEV- 2012-0208 to the CRG and the grant ANR-10-LABX-0030-INRT, which is a French State fund managed by the Agence Nationale de la Recherche under the frame programme Investissements d’Avenir ANR-10-IDEX-0002-02 to the IGBMC

The DNA damage and the DNA replication checkpoints converge at the MBF transcription factor

In fission yeast cells, Cds1 is the effector kinase of the DNA replication checkpoint. We previously showed that when the DNA replication checkpoint is activated, the repressor Yox1 is phosphorylated and inactivated by Cds1, resulting in activation of MluI-binding factor (MBF)-dependent transcription. This is essential to reinitiate DNA synthesis and for correct G1-to-S transition. Here we show that Cdc10, which is an essential part of the MBF core, is the target of the DNA damage checkpoint. When fission yeast cells are treated with DNA-damaging agents, Chk1 is activated and phosphorylates Cdc10 at its carboxy-terminal domain. This modification is responsible for the repression of MBF-dependent transcription through induced release of MBF from chromatin. This inactivation of MBF is important for survival of cells challenged with DNA-damaging agents. Thus Yox1 and Cdc10 couple normal cell cycle regulation in unperturbed conditions and the DNA replication and DNA damage checkpoints into a single transcriptional complex.This work was supported by grants from the Spanish Ministry of Science and Innovation (BFU2009–07453 and BFU2012-31939), PLAN E and FEDER, Consolider-Ingenio 2007–0020, and SGR2009-195 from the Generalitat de Catalunya. J.A. and E.H. are recipients of ICREA Academia Awards (Generalitat de Catalunya