Mutant Telomeric Repeats in Yeast Can Disrupt the Negative Regulation of Recombination-Mediated Telomere Maintenance and Create an Alternative Lengthening of Telomeres-Like Phenotype

Abstract

Some human cancers maintain telomeres using alternative lengthening of telomeres (ALT), a process thought to be due to recombination. In Kluyveromyces lactis mutants lacking telomerase, recombinational telomere elongation (RTE) is induced at short telomeres but is suppressed once telomeres are moderately elongated by RTE. Recent work has shown that certain telomere capping defects can trigger a different type of RTE that results in much more extensive telomere elongation that is reminiscent of human ALT cells. In this study, we generated telomeres composed of either of two types of mutant telomeric repeats, Acc and SnaB, that each alter the binding site for the telomeric protein Rap1. We show here that arrays of both types of mutant repeats present basally on a telomere were defective in negatively regulating telomere length in the presence of telomerase. Similarly, when each type of mutant repeat was spread to all chromosome ends in cells lacking telomerase, they led to the formation of telomeres produced by RTE that were much longer than those seen in cells with only wild-type telomeric repeats. The Acc repeats produced the more severe defect in both types of telomere maintenance, consistent with their more severe Rap1 binding defect. Curiously, although telomerase deletion mutants with telomeres composed of Acc repeats invariably showed extreme telomere elongation, they often also initially showed persistent very short telomeres with few or no Acc repeats. We suggest that these result from futile cycles of recombinational elongation and truncation of the Acc repeats from the telomeres. The presence of extensive 3 overhangs at mutant telomeres suggests that Rap1 may normally be involved in controlling 5 end degradation.

Rap1 in Candida albicans: an Unusual Structural Organization and a Critical Function in Suppressing Telomere Recombination

“…Our findings thus demonstrate for the first time a novel function for Rap1 in suppressing telomere recombination. Notably, K. lactis mutants with aberrant telomere repeats that cannot be bound by Rap1 have also been reported to experience high levels of telomere recombination (4). It is thus tempting to suggest that Rap1 mediates a conserved function in regulating abnormal telomere recombination in C. albicans and K. lactis.…”

Survey of Arabidopsis- and Human-type Telomere Repeats in Plants Using Fluorescence in situ Hybridisation

“…Telomeres are constructed with telomere repeats, as well as specific proteins (Cech 2004), and are important in controlling chromosome positions in the nucleus (Naito et al 1998, Riha et al 2001, Bechard et al 2009). Telomere repeats have been reported in many taxa.…”

Evidence for an Additional Base-Pairing Element between the Telomeric Repeat and the Telomerase RNA Template in Kluyveromyces lactis and Other Yeasts

“…The ter1-24T(SnaB) mutation (which creates a SnaBI restriction site) has been the most extensively studied of this group. When tandem 24T(SnaB) repeats are inserted basally at an otherwise wild-type telomere, that telomere becomes abnormally long (1). This indicates that 24T(SnaB) repeats are defective at negatively regulating telomere length as would be expected for a Rap1 binding defect.…”