Chromosome-specific telomere lengths and the minimal functional telomere revealed by nanopore sequencing.

We developed a method to tag telomeres and measure telomere length by nanopore sequencing in the yeast Nanopore allows long-read sequencing through the telomere, through the subtelomere, and into unique chromosomal sequence, enabling assignment of telomere length to a specific chromosome end. We observed chromosome end-specific telomere lengths that were stable over 120 cell divisions. These stable chromosome-specific telomere lengths may be explained by slow clonal variation or may represent a new biological mechanism that maintains equilibrium unique to each chromosome end. We examined the role of and in telomere length regulation and found that is epistatic to at most telomeres, consistent with the literature. However, at telomeres that lack subtelomeric Y' sequences, double mutants had a very small, but significant, increase in telomere length compared with the single mutant, suggesting an influence of Y' elements on telomere length regulation. We sequenced telomeres in a telomerase-null mutant () and found the minimal telomere length to be ∼75 bp. In these mutants, there were apparent telomere recombination events at individual telomeres before the generation of survivors, and these events were significantly reduced in double mutants. The rate of telomere shortening in the absence of telomerase was similar across all chromosome ends at ∼5 bp per generation. This new method gives quantitative, high-resolution telomere length measurement at each individual chromosome end and suggests possible new biological mechanisms regulating telomere length.