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. Author manuscript; available in PMC: 2017 Apr 9.
Published in final edited form as: Nat Rev Mol Cell Biol. 2016 May 11;17(6):364–378. doi: 10.1038/nrm.2016.43

Figure 1. Overview of telomere composition and function.

Figure 1

Mammalian telomeres are composed of long stretches of TTAGGG repeats that range from 5 kb in human cells to 100 kb in mice and end with a single-stranded 3′ overhang of up to a few hundred nucleotides in length4,5. Telomeric DNA is bound by the specialized shelterin complex, transcribed into a long non-coding telomeric repeat-containing RNA (TERRA) and packaged into a t-loop (telomere loop) configuration. Shelterin subunits include TRF1 (telomere repeat-binding factor 1), TRF2, TIN2 (TRF1-interaction factor 2), RAP1 (repressor activator protein 1), TPP1 and POT1 (protection of telomere 1; POT1A and POT1B in mice). The six-subunit complex protects chromosome ends from DNA damage signalling by ATM (ataxia telangiectasia mutated) and ATR (ataxia telangiectasia and Rad3-related), and from DNA repair by c-NHEJ (classical non-homologous end joining), alt-NHEJ (alternative non-homologous end joining), HR (homologous recombination) and DNA end resection.