Badugu, S. | Search bioRxiv

bioRxiv2026

DNA methylation links lagging strand replication to transposable element control

DNA methylation is an essential epigenetic mark that silences transposable elements (TEs) in mammalian genomes1,2. Following DNA replication, methylation patterns must be faithfully restored3,4, yet how the two processes are coordinated remains unclear. Here, using strand-specific, genome-wide analyses5-7 in mouse embryonic stem cells, we show that DNA methylation maintenance is coupled to the lagging-strand synthesis in TE-rich regions. Paradoxically, despite this targeting, the lagging strand is more permissive for TE integration than the leading strand. Notably, insertions of full-length LINE-1s, SINEs, and satellite repeats are all enriched on the lagging strand over evolutionary time. Consequently, most TEs, particularly young elements, are oriented head-on relative to replication forks in the mouse genome, creating an unfavorable genomic configuration8 that is preferentially targeted by DNA methylation maintenance. Mechanistically, DNA methylation maintenance is coupled to the lagging-strand replication via UHRF1-LIG19 and PCNA-PAF1510 interactions, and the interference in this mechanism slows Okazaki fragment maturation, and thereby potentially may facilitate TE retention. Together, we show a mechanism of TE control during DNA replication with an unexpected evolutionary interplay in which DNA methylation may facilitate, rather than solely prevent, TE expansion.

Molecular Biology↗

bioRxiv2024

Saccharomyces cerevisiae Rev7 regulates DSB repair pathway choice through binding and blocking Mre11 nuclease and Rad50 ATPase activities

Recent studies have shown that, in human cancer cells, the tetrameric Shieldin complex (comprising REV7, SHLD1, SHLD2, and SHLD3) facilitates non-homologous end-joining (NHEJ) while blocking homologous recombination (HR). Surprisingly, several eukaryotic species lack SHLD1, SHLD2 and SHLD3 orthologs, suggesting that Rev7 may leverage an alternative mechanism to regulate the double-strand break (DSB) repair pathway choice. Exploring this hypothesis, we discovered that Saccharomyces cerevisiae Rev7 physically interacts with the Mre11-Rad50-Xrs2 (MRX) subunits, impedes G-quadruplex DNA synergised-HU-induced toxicity and facilitates NHEJ, while antagonizing HR. Notably, we reveal that a 42-amino acid C-terminal fragment of Rev7 binds to the subunits of MRX complex, protects rev7{Delta} cells from G-quadruplex DNA-HU-induced toxicity, and promotes NHEJ by blocking HR. By comparison, the N-terminal HORMA domain, a conserved protein-protein interaction module, was dispensable. We further show that the full-length Rev7 impedes Mre11 nuclease and Rad50s ATPase activities without affecting the latters ATP-binding ability. Combined, these results provide unanticipated insights into the functional interaction between the MRX subunits and Rev7 and highlight a mechanism by which Rev7 facilitates DSB repair via NHEJ, and attenuation of HR, by blocking Mre11 nuclease and Rad50s ATPase activities in S. cerevisiae. IMPACT STATEMENTThe mechanisms steering DNA double-strand break repair pathway choice is a topic of intense investigation, but remains incompletely understood. Our findings suggest that yeast Rev7 promotes DSB repair via NHEJ and inhibits homologous recombination by blocking Mre11 nuclease and Rad50s ATPase activities.

molecular biology↗