Telomeric circles are abundant in the stn1-M1 mutant that maintains its telomeres through recombination.
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.
Department of Genetics, University of Georgia, Athens, GA 30602, USA.
Evelina Y
EY
Basenko
Anthony J
AJ
Cesare
Shilpa
S
Iyer
Jack D
JD
Griffith
Michael J
MJ
McEachern
D004270:DNA, Circular / Q000032:analysis / Q000648:ultrastructure*; D015180:Electrophoresis, Gel, Two-Dimensional; D007716:Kluyveromyces / Q000235:genetics; D009154:Mutation; D011995:Recombination, Genetic; D016615:Telomere / Q000737:chemistry* / Q000648:ultrastructure
D004270:DNA, Circular