MRE11 proximal polyadenylation site-mediated looping impacts transcription and genomic stability.

Alternative polyadenylation (APA) generates transcript isoforms with variable 3' untranslated regions (UTR) lengths, yet its role in DNA damage response (DDR) genes is poorly understood. Here, we demonstrate that the proximal polyadenylation site (pPAS) of MRE11 engages in PAS-promoter looping to facilitate RNA polymerase recycling and sustain high promoter activity-a mechanism not well characterized in mammals. Deletion of the MRE11 pPAS disrupts this looping, reduces MRE11 transcription, impairs MRE11-RAD50-NBS1 (MRN) complex levels, and phenocopies hypomorphic MRE11 mutations. MRE11pPAS-/- cells exhibit ectopic DNA replication and reduced viability under overgrowth conditions. 5-ethynyl-2'-deoxyuridine sequencing (EdU-seq) revealed aberrant DNA synthesis occurring primarily at intronic and intergenic regions, where MRE11 chromatin immunoprecipitation sequencing (ChIP-seq) showed decreased binding correlating with elevated replication. Furthermore, multiple DDR genes with several PASs also form PAS-promoter loops, suggesting a broader regulatory mechanism. Together these findings identify the MRE11 pPAS as a critical noncoding element that maintains genome stability through transcriptional regulation via PAS-promoter looping.