Abstract Ends of linear chromosomes require protection from host repair machinery that otherwise will mistake them for damaged DNA. The E. coli bacteriophage N15 harbors a linear genome with covalently closed hairpin ends formed by the phage-encoded telomere resolvase TelN. The double-strand break repair complex Mre11-Rad50 (MR, SbcCD in E. coli ) specifically targets DNA termini, yet how hairpin telomeres evade host nuclease degradation in bacteria remains unknown. Here, we demonstrate that TelN is essential and sufficient to protect N15 phage-derived hairpin telomeres from MR processing in E. coli . Using a combination of genetic and biochemical approaches, we show that this protective function requires both TelN sequence-specific DNA binding and species-specific protein-protein interactions. Notably, we found that protection is independent of TelN’s resolution activity and does not require the C-terminal domains of TelN. Our findings reveal a potentially broad mechanism of telomere protection, providing insights into a conserved regulation of MR activity at chromosome ends across the tree of life.
Houmel et al. (2025) studied this question.