Smolikov Sarit, Krauskopf Anat
Department of Molecular Microbiology and Biotechnology, Tel-Aviv University, Tel Aviv 69978, Israel.
Mol Cell Biol. 2003 Dec;23(23):8729-39. doi: 10.1128/MCB.23.23.8729-8739.2003.
Telomeres are nucleoprotein structures that cap the ends of chromosomes and thereby protect their stability and integrity. In the presence of telomerase, the enzyme that synthesizes telomeric repeats, telomere length is controlled primarily by Rap1p, the budding yeast telomeric DNA binding protein which, through its C-terminal domain, nucleates a protein complex that limits telomere lengthening. In the absence of telomerase, telomeres shorten with every cell division, and eventually, cells enter replicative senescence. We have set out to identify the telomeric property that determines the replicative capacity of telomerase-deficient budding yeast. We show that in cells deficient for both telomerase and homologous recombination, replicative capacity is dependent on telomere length but not on the binding of Rap1p to the telomeric repeats. Strikingly, inhibition of Rap1p binding or truncation of the C-terminal tail of Rap1p in Kluyveromyces lactis and deletion of the Rap1p-recruited complex in Saccharomyces cerevisiae lead to a dramatic increase in replicative capacity. The study of the role of telomere binding proteins and telomere length on replicative capacity in yeast may have significant implications for our understanding of cellular senescence in higher organisms.
端粒是一种核蛋白结构，它覆盖在染色体末端，从而保护其稳定性和完整性。在端粒酶（一种合成端粒重复序列的酶）存在的情况下，端粒长度主要由Rap1p控制，Rap1p是芽殖酵母端粒DNA结合蛋白，它通过其C末端结构域形成一个限制端粒延长的蛋白质复合物。在没有端粒酶的情况下，端粒会随着每次细胞分裂而缩短，最终细胞进入复制性衰老。我们着手确定决定端粒酶缺陷型芽殖酵母复制能力的端粒特性。我们发现，在端粒酶和同源重组均缺陷的细胞中，复制能力取决于端粒长度，而不取决于Rap1p与端粒重复序列的结合。令人惊讶的是，在乳酸克鲁维酵母中抑制Rap1p结合或截短Rap1p的C末端尾巴，以及在酿酒酵母中删除Rap1p募集的复合物，都会导致复制能力显著增加。研究端粒结合蛋白和端粒长度在酵母复制能力中的作用，可能对我们理解高等生物中的细胞衰老具有重要意义。
