In response to DNA damage, checkpoint signalling protects genome integrity at the cost of repressing cell cycle progression and DNA replication. Mechanisms for checkpoint down-regulation are therefore necessary for proper cellular proliferation. We recently uncovered a phosphatase-independent mechanism for dampening checkpoint signalling, where the checkpoint adaptor Rad9 is counteracted by the repair scaffolds Slx4-Rtt107. Here, we establish the molecular requirements for this new mode of checkpoint regulation. We engineered a minimal multi-BRCT-domain (MBD) module that recapitulates the action of Slx4-Rtt107 in checkpoint down-regulation. MBD mimics the damage-induced Dpb11-Slx4-Rtt107 complex by synergistically interacting with lesion-specific phospho-sites in Ddc1 and H2A. We propose that efficient recruitment of Dpb11-Slx4-Rtt107 or MBD via a cooperative 'two-site-docking' mechanism displaces Rad9. MBD also interacts with the Mus81 nuclease following checkpoint dampening, suggesting a spatio-temporal coordination of checkpoint signalling and DNA repair via a combinatorial mode of BRCT-domains interactions.

Recurrent somatic mutations of H3F3A in aggressive pediatric high-grade gliomas generate K27M or G34R/V mutant histone H3.3. H3.3-G34R/V mutants are common in tumors with mutations in p53 and ATRX, an H3.3-specific chromatin remodeler. To gain insight into the role of H3-G34R, we generated fission yeast that express only the mutant histone H3. H3-G34R specifically reduces H3K36 tri-methylation and H3K36 acetylation, and mutants show partial transcriptional overlap with set2 deletions. H3-G34R mutants exhibit genomic instability and increased replication stress, including slowed replication fork restart, although DNA replication checkpoints are functional. H3-G34R mutants are defective for DNA damage repair by homologous recombination (HR), and have altered HR protein dynamics in both damaged and untreated cells. These data suggest H3-G34R slows resolution of HR-mediated repair and that unresolved replication intermediates impair chromosome segregation. This analysis of H3-G34R mutant fission yeast provides mechanistic insight into how G34R mutation may promote genomic instability in glioma.DOI: http://dx.doi.org/10.7554/eLife.27406.001

Noncoding small RNAs play diverse, important biological roles through gene expression regulation. However, their low expression levels make it difficult to identify new small RNA species and study their functions, calling for the development of detection schemes with higher simplicity, sensitivity, and specificity. Herein, we reported a straightforward assay that combined the stand-alone rolling circle amplification (RCA) with capillary electrophoresis (CE) for specific and sensitive detection of small RNAs in biological samples. In order to enhance the overall reaction efficiency and simplify the procedure, RCA was not preceded with ligation, and a preformed circular probe was employed as the template for the target small RNA-primed isothermal amplification. The long RCA product was digested and analyzed by CE. Two DNA polymerases, the Phi29 and Bst, were compared for their detection performance. Bst is superior in the aspects of specificity, procedure simplicity, and reproducibility, while Phi29 leads to a 5-fold lower detection limit and is able to detect as low as 35 amol of the target small RNA. Coamplification of an internal standard with the target and employment of the RNase A digestion step allow accurate and reproducible quantification of low amounts of small RNA targets spiked into hundreds of nanograms of the plant total RNA extract with a recovery below 110% using either enzyme. Our assay can be adapted to a capillary array system for high-throughput screening of small RNA expression in biological samples. Also, the one-step isothermal process has the potential to conveniently amplify a very limited amount of the RNA samples, e.g., RNA extracted from only a few cells, inside the capillary column or on a microchip.