Krauskopf A, Blackburn E H
Department of Microbiology and Immunology, University of California, San Francisco, CA 94143-0414, USA.
Proc Natl Acad Sci U S A. 1998 Oct 13;95(21):12486-91. doi: 10.1073/pnas.95.21.12486.
Telomere length is maintained through a dynamic balance between addition and loss of the terminal telomeric DNA. Normal telomere length regulation requires telomerase as well as a telomeric protein-DNA complex. Previous work has provided evidence that in the budding yeasts Kluyveromyces lactis and Saccharomyces cerevisiae, the telomeric double-stranded DNA binding protein Rap1p negatively regulates telomere length, in part by nucleating, by its C-terminal tail, a higher-order DNA binding protein complex that presumably limits access of telomerase to the chromosome end. Here we show that in K. lactis, truncating the Rap1p C-terminal tail (Rap1p-DeltaC mutant) accelerates telomeric repeat turnover in the distal region of the telomere. In addition, combining the rap1-DeltaC mutation with a telomerase template mutation (ter1-kpn), which directs the addition of mutated telomeric DNA repeats to telomeres, synergistically caused an immediate loss of telomere length regulation. Capping of the unregulated telomeres of these double mutants with functionally wild-type repeats restored telomere length control. We propose that the rate of terminal telomere turnover is controlled by Rap1p specifically through its interactions with the most distal telomeric repeats.
端粒长度通过末端端粒DNA的添加和丢失之间的动态平衡得以维持。正常的端粒长度调控需要端粒酶以及一种端粒蛋白质-DNA复合物。先前的研究表明，在芽殖酵母乳酸克鲁维酵母和酿酒酵母中，端粒双链DNA结合蛋白Rap1p对端粒长度起负调控作用，部分原因是其C末端尾巴能促使一种高阶DNA结合蛋白复合物形成，该复合物可能会限制端粒酶接近染色体末端。在此我们表明，在乳酸克鲁维酵母中，截短Rap1p的C末端尾巴（Rap1p-ΔC突变体）会加速端粒远端区域的端粒重复序列更替。此外，将rap1-ΔC突变与端粒酶模板突变（ter1-kpn）相结合，后者会导致向端粒添加突变的端粒DNA重复序列，二者协同作用会立即导致端粒长度调控丧失。用功能上野生型的重复序列封端这些双突变体不受调控的端粒可恢复端粒长度控制。我们提出，末端端粒更替的速率由Rap1p通过其与最远端端粒重复序列的相互作用特异性地控制。
