Telomeres are repeated sequences found at the end of the linear chromosomes of most eukaryotes and are required for chromosome integrity. Expression of the reverse-transcriptase telomerase allows for extension of telomeric repeats to counteract natural telomere shortening. Although Chlamydomonas reinhardtii, a photosynthetic unicellular green alga, is widely used as a model organism in photosynthesis and flagella research, and for biotechnological applications, the biology of its telomeres has not been investigated in depth. Here, we show that the C. reinhardtii (TTTTAGGG)_n telomeric repeats are mostly nondegenerate and that the telomeres form a protective structure, with a subset ending with a 3' overhang and another subset presenting a blunt end. Although telomere size and length distributions are stable under various standard growth conditions, they vary substantially between 12 genetically close reference strains. Finally, we identify CrTERT, the gene encoding the catalytic subunit of telomerase and show that telomeres shorten progressively in mutants of this gene. Telomerase mutants eventually enter replicative senescence, demonstrating that telomerase is required for long-term maintenance of telomeres in C. reinhardtii.

中文翻译：

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莱茵衣藻端粒和端粒酶突变体的分子表征。

端粒是在大多数真核生物的线性染色体末端发现的重复序列，是染色体完整性所必需的。逆转录酶端粒酶的表达允许端粒重复序列的延伸以抵消天然端粒的缩短。尽管光合单细胞绿藻衣藻被广泛用作光合作用和鞭毛研究的模型生物，并且在生物技术应用中，其端粒的生物学尚未得到深入研究。在这里，我们显示莱茵衣藻（TTTTAGGG）_n端粒重复大部分是简并的，端粒形成保护性结构，一个亚基以3'突出端结束，另一个亚基呈现平末端。尽管端粒的大小和长度分布在各种标准生长条件下都是稳定的，但它们在12个遗传接近的参考菌株之间有很大差异。最后，我们鉴定出CrTERT，该基因编码端粒酶的催化亚基，并表明端粒在该基因的突变体中逐渐缩短。端粒酶突变体最终进入复制衰老，表明端粒酶是莱因氏梭菌中端粒长期维持所必需的。