T-circles and t-loops play a role in Kluveromyces lactis recombinational telomere elongation
Groff-Vindman, Cindy Sue
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Recombinational telomere elongation (RTE) known as ALT (alternate lengthening oftelomeres) is the mechanism of telomere maintenance in up to 5-10% of human cancers. Thetelomeres of yeast mutants lacking telomerase can also be maintained by recombination. Theroll-and-spread model has been proposed to explain this elongation in the yeast Kluveromyceslactis. Our model suggests that a very small (<100 bp) circular molecule of telomeric DNA iscopied by a rolling circle event to generate a single long telomere. The sequence of this primaryelongated telomere is then spread by recombination to all remaining telomeres. Data presentedhere will show that K. lactis cells can efficiently utilize synthetic single-stranded telomericcircles of 100 nt to elongate there telomeres. It is also shown here, by 2D gel analysis andelectron microscopy, that small circles of single and double-stranded telomeric DNA (t-circles)are commonly made by recombination in a K. lactis mutant with long telomeres. To ourknowledge this is the first report of single-stranded t-circles as a product of telomeredysfunction. We also present evidence that t-loop structures like those originally isolated fromhuman cells are present on some K. lactis telomeres. Our data shows phenotypic similaritiesbetween the telomeres found in ter1-16T and those previously analyzed in human ALT cells.