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. 2020 Feb 28;12(3):558. doi: 10.3390/cancers12030558

Figure 3.

Figure 3

Representation of shelterin complex, heterotrimeric complex CST, and telomeric repeat containing RNA (TERRA). Shelterin complex comprises of six distinct protein subunits: telomeric-repeat-binding factor 1 and 2 (TRF1 and TRF2), TRF1-interacting nuclear protein 2 (TIN2), protection of telomeres 1 (POT1), POT1 and TIN2-interacting protein (TPP1), and repressor and activator protein 1 (RAP1). TRF1 and TRF2 bind the double-stranded DNA; POT1 binds the single-stranded 3′ G-overhang. TIN2 bridges TRF1 and TRF2 by binding to both the proteins simultaneously through independent domains and recruits TPP1–POT1 complex. RAP1 interacts with TRF2 to localize at the telomeres. CST complex is a heterotrimeric protein consisting of conserved telomere protection component 1 (CTC1), suppressor of cdc13 a (STN1), and telomeric pathway with STN1 (TEN1), which specifically localize to the single-stranded 3′ overhang and protect the telomeres by mediating DNA replication and telomerase regulation, independent of shelterin complex. Telomeric repeat containing RNA (TERRA) transcription initiates within subtelomeres in the direction of telomeres. TERRA is involved in regulating telomere capping and the maintenance of telomeres. Adapted from [13].