t-loops at trypanosome telomeres

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Abstract

Mammalian telomeres form large duplex loops (t-loops) that may sequester chromosome ends by invasion of the 3′ TTAGGG overhang into the duplex TTAGGG repeat array. Here we document t-loops in Trypanosoma brucei, a kinetoplastid protozoan with abundant telomeres due to the presence of many minichromosomes. These telomeres contained 10-20 kb duplex TTAGGG repeats and a 3′ TTAGGG overhang. Electron microscopy of psoralen/UV cross-linked DNA revealed t-loops in enriched telomeric restriction fragments and at the ends of isolated minichromosomes. In mammals, t-loops are large (up to 25 kb), often comprising most of the telomere. Despite similar telomere lengths, trypanosome t-loops were much smaller (∼1 kb), indicating that t-loop sizes are regulated. Coating of non-cross-linked minichromosomes with Escherichia coli single-strand binding protein (SSB) often revealed 3′ overhangs at both telomeres and several cross-linked minichromosomes had t-loops at both ends. These results suggest that t-loops and their prerequisite 3′ tails can be formed on the products of both leading and lagging strand synthesis. We conclude that t-loops are a conserved feature of eukaryotic telomeres.

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Muñoz-Jordán, J. L., Cross, G. A. M., De Lange, T., & Griffith, J. D. (2001). t-loops at trypanosome telomeres. EMBO Journal, 20(3), 579–588. https://doi.org/10.1093/emboj/20.3.579

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