Regulation of Telomere Length

端粒是核蛋白复合物，其允许染色体末端的完全复制并将这些末端与双链断裂区分开。端粒DNA由富含TG重复序列的串联阵列组成。在人类生殖细胞和酵母中，这些重复序列的长度通过端粒酶调节延长过程和由于不完全复制或溶核降解而缩短的过程而保持几乎恒定。这两个过程是如何调节的，以给出一个恒定的端粒长度是未知的。在人体细胞中，重复序列的长度随着细胞分裂而减少，当端粒变得太短时导致细胞衰老。端粒长度信息是如何传递到细胞周期机制中的尚不清楚。我们的长期目标是使用酵母作为模型系统来理解这些过程。酵母通过计算主要端粒结合蛋白Raplp的分子数量来测量端粒长度;然而，如何计算Raplp分子仍在争论中。我们建立了一个基于酵母合成端粒的端粒长度调控模型。我们提出酵母端粒与Raplp和2个调节蛋白Riflp和Rif 2 p形成折叠结构，以计数Raplp分子并阻止延伸。短端粒的Raplp分子太少，无法形成这种结构，因此它们被拉长。其他模型表明，Sir蛋白也调节长度，我们已经设计了直接测试这种可能性的测定方法。 Tel 2 p在体内与端粒结合并调节其长度。Tel 2 p突变体改变端粒长度和细胞对单个双链断裂和其他形式的DNA损伤的反应。我们假设Tel 2 p结合端粒和双链断裂来调节DNA损伤检查点的激活。检查点蛋白Tellp和Meclp的活性表明它们参与了这些过程。 我们的具体目标是确定1）调节端粒长度的结构的蛋白质组成; 2）Tellp和Meclp是否被招募到不同长度的端粒; 3）Tel 2 p如何改变端粒长度和细胞对DNA损伤的反应，以及Tel 2 p是否在体内作用于双链断裂。

Telomeres are the nucleoprotein complexes that allow the complete replication of chromosome ends and distinguish these ends from double-strand breaks. Telomere DNA consists of tandem arrays of TG-rich repeats. The length of these repeat tracts is kept nearly constant in human germ cells and yeast by regulating the processes of lengthening, via telomerase, and shortening, due to incomplete replication or nucleolytic degradation. How these two processes are regulated to give a constant telomere length is unknown. In human somatic cells, the length of the repeats decreases as cells divide, leading to cell senescence when telomeres become too short. How telomere length information is transmitted to the cell cycle machinery is unknown. Our long-term goal is to use yeast as a model system to understand these processes. Yeast measure telomere length by counting the number of molecules of the major telomere binding protein Raplp; however, how Raplp molecules are counted is under debate. We developed a model for telomere length regulation based on our construction of yeast synthetic telomeres. We propose that yeast telomeres form a folded structure with Raplp and 2 regulatory proteins, Riflp and Rif2p, to count Raplp molecules and block elongation. Short telomeres have too few Raplp molecules to form this structure, so they are elongated. Other models suggest that Sir proteins also regulate length, and we have devised assays to directly test this possibility. Tel2p binds to telomeres in vivo and regulates their length. Tel2p mutants alter telomere length and the cellular response to a single double-strand break and other forms of DNA damage. We hypothesize that Tel2p binds to telomeres and double-strand breaks to regulate activation of DNA damage checkpoints. The activities of the checkpoint proteins Tellp and Meclp suggest that they are involved in these processes. Our specific aims are to determine 1) the protein composition of the structure that regulates telomere length; 2) if Tellp and Meclp are recruited to telomeres of different lengths; and 3) how Tel2p alters telomere length and the cellular response to DNA damage and if Tel2p acts at double-strand breaks in vivo.