t-loops at trypanosome telomeres.
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 (approximately 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.
Muñoz-Jordán
J L
JL
Laboratory of Molecular Parasitology and Laboratory of Cell Biology and Genetics, Box 159, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.
Cross
G A
GA
de Lange
T
T
Griffith
J D
JD
D000818:Animals; D001483:Base Sequence; D016054:DNA, Protozoan / Q000737:chemistry / Q000235:genetics / Q000648:ultrastructure; D008854:Microscopy, Electron; D015345:Oligonucleotide Probes / Q000235:genetics; D020080:Tandem Repeat Sequences; D016615:Telomere / Q000737:chemistry* / Q000235:genetics* / Q000648:ultrastructure; D014346:Trypanosoma brucei brucei / Q000737:chemistry* / Q000235:genetics*
D016054:DNA, Protozoan; D015345:Oligonucleotide Probes