Telomeric circles are abundant in the stn1-M1 mutant that maintains its telomeres through recombination

Nucleic Acids Res. 2010 Jan;38(1):182-9. doi: 10.1093/nar/gkp814. Epub 2009 Oct 25.

Abstract

Some human cancers maintain their telomeres using the alternative lengthening of telomeres (ALT) mechanism; a process thought to involve recombination. Different types of recombinational telomere elongation pathways have been identified in yeasts. In senescing yeast telomerase deletion (ter1-Delta) mutants with very short telomeres, it has been hypothesized that copying a tiny telomeric circle (t-circle) by a rolling circle mechanism is the key event in telomere elongation. In other cases more closely resembling ALT cells, such as the stn1-M1 mutant of Kluyveromyces lactis, the telomeres appear to be continuously unstable and routinely reach very large sizes. By employing two-dimensional gel electrophoresis and electron microscopy, we show that stn1-M1 cells contain abundant double stranded t-circles ranging from approximately 100 to 30,000 bp in size. We also observed small single-stranded t-circles, specifically composed of the G-rich telomeric strand and tailed circles resembling rolling circle replication intermediates. The t-circles most likely arose from recombination events that also resulted in telomere truncations. The findings strengthen the possibility that t-circles contribute to telomere maintenance in stn1-M1 and ALT cells.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • DNA, Circular / analysis
  • DNA, Circular / ultrastructure*
  • Electrophoresis, Gel, Two-Dimensional
  • Kluyveromyces / genetics
  • Mutation
  • Recombination, Genetic*
  • Telomere / chemistry*
  • Telomere / ultrastructure

Substances

  • DNA, Circular