biostudies-otherLimbo ONCI NIH HHSNIGMS NIH HHS1389-1399https://www.ebi.ac.uk/biostudies/studies/S-EPMC5994899The Mre11-Rad50-Nbs1 (MRN) protein complex and ATM/Tel1 kinase protect genome integrity through their functions in DNA double-strand break (DSB) repair, checkpoint signaling, and telomere maintenance. Nbs1 has a conserved C-terminal motif that binds ATM/Tel1, but the full extent and significance of ATM/Tel1 interactions with MRN are unknown. Here, we show that Tel1 overexpression bypasses the requirement for Nbs1 in DNA damage signaling and telomere maintenance. These activities require Mre11-Rad50, which localizes to DSBs and bind Tel1 in the absence of Nbs1. Fusion of the Tel1-binding motif of Nbs1 to Mre11 is sufficient to restore Tel1 signaling in nbs1? cells. Tel1 overexpression does not restore Tel1 signaling in cells carrying the rad50-I1192W mutation, which impairs the ability of Mre11-Rad50 to form the ATP-bound closed conformation. From these findings, we propose that Tel1 has a high-affinity interaction with the C-terminus of Nbs1 and a low-affinity association with Mre11-Rad50, which together accomplish efficient localization and activation of Tel1 at DSBs and telomeres.biostudies-otherEurope PMCUnknown29(11)Molecular biology of the cellPMC5994899R01 GM059447R01 CA077325R01 CA117638Russell PLimbo OYamada YfalseMre11-Rad50-dependent activity of ATM/Tel1 at DNA breaks and telomeres in the absence of Nbs1.The Mre11-Rad50-Nbs1 (MRN) protein complex and ATM/Tel1 kinase protect genome integrity through their functions in DNA double-strand break (DSB) repair, checkpoint signaling, and telomere maintenance. Nbs1 has a conserved C-terminal motif that binds ATM/Tel1, but the full extent and significance of ATM/Tel1 interactions with MRN are unknown. Here, we show that Tel1 overexpression bypasses the requirement for Nbs1 in DNA damage signaling and telomere maintenance. These activities require Mre11-Rad50, which localizes to DSBs and bind Tel1 in the absence of Nbs1. Fusion of the Tel1-binding motif of Nbs1 to Mre11 is sufficient to restore Tel1 signaling in nbs1? cells. Tel1 overexpression does not restore Tel1 signaling in cells carrying the rad50-I1192W mutation, which impairs the ability of Mre11-Rad50 to form the ATP-bound closed conformation. From these findings, we propose that Tel1 has a high-affinity interaction with the C-terminus of Nbs1 and a low-affinity association with Mre11-Rad50, which together accomplish efficient localization and activation of Tel1 at DSBs and telomeres.2018-01-01T00:00:00Z2018 Jun2019-03-26T23:51:07Z2019-03-26T23:51:07ZS-EPMC59948992985155610.1091/mbc.E17-07-0470