Prevention of DNA Rereplication Through a Meiotic Recombination Checkpoint Response

Abstract

In the budding yeast Saccharomyces cerevisiae, unnatural stabilization of the cyclin-dependent kinase inhibitor Sic1 during meiosis can trigger extra rounds of DNA replication. When programmed DNA double-strand breaks (DSBs) are generated but not repaired due to absence of DMC1, a pathway involving the checkpoint gene RAD17 prevents this DNA rereplication. Further genetic analysis has now revealed that prevention of DNA rereplication also requires MEC1, which encodes a protein kinase that serves as a central checkpoint regulator in several pathways including the meiotic recombination checkpoint response. Downstream of MEC1, MEK1 is required through its function to inhibit repair between sister chromatids. By contrast, meiotic recombination checkpoint effectors that regulate gene expression and cyclin-dependent kinase activity are not necessary. Phosphorylation of histone H2A, which is catalyzed by Mec1 and the related Tel1 protein kinase in response to DSBs, and can help coordinate activation of the Rad53 checkpoint protein kinase in the mitotic cell cycle, is required for the full checkpoint response. Phosphorylation sites that are targeted by Rad53 in a mitotic S phase checkpoint response are also involved, based on the behavior of cells containing mutations in the DBF4 and SLD3 DNA replication genes. However, RAD53 does not appear to be required, nor does RAD9, which encodes a mediator of Rad53, consistent with their lack of function in the recombination checkpoint pathway that prevents meiotic progression. While this response is similar to a checkpoint mechanism that inhibits initiation of DNA replication in the mitotic cell cycle, the evidence points to a new variation on DNA replication control.

SUMO is a pervasive regulator of meiosis

“…Mec1/Tel1-mediated H2A-S128 phosphorylation (γ-H2A) plays important roles in the DNA damage response ( Downs et al, 2000 ; Morrison et al, 2004 ; Redon et al, 2003 ; van Attikum et al, 2004 ). In yeast meiosis, γ-H2A is initially triggered in S-phase ( Cheng et al, 2013 ) and contributes to a checkpoint that prevents re-replication ( Najor et al, 2016 ). In our dataset, Hta1 (H2A1) K123 SUMOylation was only observed on a peptide that was also phosphorylated at either at T125 or S128.…”

Delineation of the SUMO-Modified Proteome Reveals Regulatory Functions Throughout Meiosis

“…Histone H2A: Mec1/Tel1-mediated H2A-S128 phosphorylation (γ-H2A) plays important roles in the DNA damage response (Downs et al, 2000;Morrison et al, 2004;Redon et al, 2003;van Attikum et al, 2004). In yeast meiosis, γ-H2A is initially triggered in S-phase (Cheng et al, 2013) and contributes to a checkpoint that prevents re-replication (Najor et al, 2016). In our dataset, Hta1 (H2A1) K123 SUMOylation was only observed on a peptide that was also phosphorylated at either at T125 or S128.…”

“…Acetylation of H3, especially at K14, is involved in Gcn5-dependent transcriptional activation and SUMOylation may modulate this activity (Grant et al, 1999;Suka et al, 2001). Dot1-catalyzed H3-K79 methylation facilitates meiotic checkpoint activation, promotes DSB formation when H3-K4 is mutated, and helps prevent re-replication in combination with γ-H2A (Bani Ismail et al, 2014;Najor et al, 2016;Ontoso et al, 2013). SUMOylation was also detected at H3-K79 suggesting antagonism of these activities.…”