Project description:G-quadruplexes (G4s) are prevalent DNA structures that regulate transcription but also threaten genome stability. How G4 dynamics is controlled remains poorly understood. Here, we report that RNA transcripts govern G4 landscapes through coordinated ‘G-loop’ assembly and disassembly. G-loop assembly involves activation of the ATM and ATR kinases followed by homology-directed invasion of RNA opposite the G4 strand mediated by BRCA2 and RAD51. Disassembly of the G-loop resolves the G4 structure via DHX36-FANCJ-mediated G4 unwinding that triggers nucleolytic incision and subsequent hybrid strand renewal by DNA synthesis. Inhibition of G-loop disassembly causes global G4 and R-loop accumulation, leading to transcriptome dysregulation, replication stress, and genome instability. These findings establish an intricate G-loop assembly-disassembly mechanism that controls G4 landscapes and is essential for cellular homeostasis and survival.
Project description:DNA G-quadruplexes (G4s) are secondary structures with significant roles in regulating genome function and stability. Dysregulation of the dynamic formation of G4s is linked to genomic instability and disease, but the underlying mechanisms are not fully understood. In this study, we conducted a screen of chromatin-modifying enzymes and identified nine potential inhibitors of G4 formation, including seven that were not previously characterized. Among these, we highlight the role of BAZ2 chromatin remodelers as key suppressors of G4 DNA and G4-related genome instability. Depletion of BAZ2 subunits led to increased G4 formation, especially at transcriptional regulatory elements. BAZ2B was found to associate with G4 loci, suggesting that it plays a direct role in suppressing G4s. While BAZ2-deficient cells exhibited modest genomic instability, treatment with the G4-stabilizing ligand BRACO19 exacerbated double-strand breaks (DSBs), highlighting its utility as a tool to study G4-dependent genome instability. DSB profiling using INDUCE-seq uncovered distinct breakage patterns around G4s, further underscoring the impact of G4s on genome integrity. Notably, we found that within G4s, G repeats were more susceptible to DSBs than loops. These results establish BAZ2 chromatin remodeling complexes as direct regulators of G4 dynamics and provide new insights into G4-dependent genome instability.
Project description:G-quadruplexes (G4s) form throughout the genome and influence important cellular processes, but their deregulation can challenge DNA replication fork progression and threaten genome stability. Here, we demonstrate an unexpected, dual role for the dsDNA translocase HLTF in G4 metabolism. First, we find that HLTF is enriched at G4s in the human genome and suppresses G4 accumulation throughout the cell cycle using its ATPase activity. This function of HLTF affects telomere maintenance by restricting alternative lengthening of telomeres, a process stimulated by G4s. We also show that HLTF and MSH2, a mismatch repair factor that binds G4s, act in independent pathways to suppress G4s and to promote resistance to G4 stabilization. In a second, distinct role, HLTF restrains DNA synthesis upon G4 stabilization by suppressing PrimPol-dependent repriming. Together, the dual functions of HLTF in the G4 response prevent DNA damage and potentially mutagenic replication to safeguard genome stability.
