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t-loops at trypanosome telomeres
J L Muñoz-Jordán1, G A Cross, T de Lange
1Laboratory of Molecular Parasitology and Laboratory of Cell Biology and Genetics, Box 159, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.
The EMBO Journal
|February 7, 2001
Summary
Telomere loops (t-loops) are conserved across eukaryotes. In Trypanosoma brucei, these structures form at chromosome ends, suggesting a common mechanism for telomere protection in diverse organisms.
Area of Science:
- Cell Biology
- Genetics
- Molecular Biology
Background:
- Mammalian telomeres protect chromosome ends via large duplex loops (t-loops).
- These t-loops involve the 3' TTAGGG overhang invading the duplex repeat array.
- Trypanosoma brucei possesses abundant telomeres on numerous minichromosomes.
Purpose of the Study:
- To investigate the presence and characteristics of t-loops in Trypanosoma brucei.
- To determine if t-loops are a conserved feature of eukaryotic telomeres.
- To explore the regulation of t-loop size and formation.
Main Methods:
- Electron microscopy of psoralen/UV cross-linked DNA.
- Analysis of enriched telomeric restriction fragments.
- Isolation and examination of minichromosomes.
- Use of Escherichia coli single-strand binding protein (SSB).
Main Results:
- T-loops were identified in Trypanosoma brucei telomeres, characterized by 10-20 kb TTAGGG repeats and a 3' overhang.
- Trypanosome t-loops were significantly smaller (approx. 1 kb) than mammalian t-loops, indicating size regulation.
- T-loops and 3' overhangs were observed at both telomeres of minichromosomes, suggesting formation on both leading and lagging strand synthesis products.
Conclusions:
- T-loops are a conserved feature of eukaryotic telomeres.
- Telomere loop formation is a fundamental mechanism for chromosome end protection.
- T-loop size is subject to regulation, even with similar telomere lengths across species.