Long-read sequencing infers a mechanism for copy number variation of template for alternative lengthening of telomeres in a wild C. elegans strain

Template for alternative lengthening of telomeres 1 (TALT1) is a specific sequence used to protect chromosomal ends from telomere damage first identified in the CB4856 strain of Caenorhabditis elegans . Here we assembled the genome of DL226, a wild strain with one more copy of TALT1-like sequences in its genome compared to those of CB4856, using long-read DNA sequencing. We found that a five-copy array of short telomeric repeats and TALT1s present in CB4856 were changed to a six-copy array due to the duplication of the third copy; there was an additional damage-repair trace in the new short telomeric repeat near the newly replicated TALT1.