Nucleic Acids Research Advance Access published online on October 25, 2009
Nucleic Acids Research, doi:10.1093/nar/gkp814
Molecular Biology |
Telomeric circles are abundant in the stn1-M1 mutant that maintains its telomeres through recombination
1Department of Genetics, Fred C. Davison Life Science Complex, University of Georgia, Athens, GA 30602 and 2Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC 27599, USA
*To whom correspondence should be addressed. Tel: +1 706 542 1821; Fax: +1 706 542 3910; Email: mjm{at}uga.edu
Received February 6, 2009. Revised September 15, 2009. Accepted September 15, 2009.
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-
) 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 
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.
Present addresses: Shilpa Iyer, Center for the Study of Neurodegenerative diseases, PO Box 800394, Charlottesville, VA 22908, USA.
Anthony Cesare, Children’s Medical Research Institute, Westmead, New South Wales 2150, Australia.
The authors wish it to be known that, in their opinion, the first two authors should be regarded as joint First Authors.