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. Author manuscript; available in PMC: 2022 Oct 1.
Published in final edited form as: Crit Rev Biochem Mol Biol. 2021 Jun 20;56(5):441–454. doi: 10.1080/10409238.2021.1925218

Figure 4. Role of Tel1 at double-stranded DNA breaks and telomeres.

Figure 4.

Damage-induced dsDNA breaks signal the recruitment of Tel1 by MRX. Only the ATP-form of Rad50 is competent for activation of Tel1. Activated Tel1 initiates a checkpoint by phosphorylating targets including Rad53 and Chk1. Tel1 additionally targets other factors that initiate DNA resection, which leads to a Mec1-dependent checkpoint response. Rif2 regulates telomere lengths by binding Rap1 and acting on Rad50. At a long telomere (bottom), the increased local concentration of Rif2 discharges the ATP-bound form of Rad50, thereby suppressing Tel1 activity, and promoting dissociation of Tel1 and MRX. At a short telomere (top), the relative lack of Rif2 allows Tel1-MRX activation of telomerase, resulting in telomere elongation.