Wright W E, Tesmer V M, Huffman K E, Levene S D, Shay J W
Department of Cell Biology and Neuroscience, The University of Texas Southwestern Medical Center, Dallas, Texas 75235-9039 USA.
Genes Dev. 1997 Nov 1;11(21):2801-9. doi: 10.1101/gad.11.21.2801.
Telomeres protect the ends of linear chromosomes from degradation and abnormal recombination events, and in vertebrates may be important in cellular senescence and cancer. However, very little is known about the structure of human telomeres. In this report we purify telomeres and analyze their termini. We show that following replication the daughter telomeres have different terminal overhangs in normal diploid telomerase-negative human fibroblasts. Electron microscopy of those telomeres that have long overhangs yields 200 +/- 75 nucleotides of single-stranded DNA. This overhang is four times greater than the amount of telomere shortening per division found in these cells. These results are consistent with models of telomere replication in which leading-strand synthesis generates a blunt end while lagging-strand synthesis produces a long G-rich 3' overhang, and suggest that variations in lagging-strand synthesis may regulate the rate of telomere shortening in normal diploid human cells. Our results do not exclude the possibility that nuclease processing events following leading strand synthesis result in short overhangs on one end.
端粒可保护线性染色体的末端免受降解和异常重组事件的影响，在脊椎动物中，端粒可能在细胞衰老和癌症中起重要作用。然而，人们对人类端粒的结构知之甚少。在本报告中，我们纯化了端粒并分析了它们的末端。我们发现，在正常二倍体端粒酶阴性的人类成纤维细胞中，复制后的子代端粒具有不同的末端悬突。对那些具有长悬突的端粒进行电子显微镜观察，发现单链DNA长度为200±75个核苷酸。这种悬突比这些细胞中每次分裂时端粒缩短的量大四倍。这些结果与端粒复制模型一致，即前导链合成产生平端，而后随链合成产生长的富含G的3'悬突，并表明后随链合成的变化可能调节正常二倍体人类细胞中端粒缩短的速率。我们的结果并不排除在前导链合成后核酸酶加工事件导致一端出现短悬突的可能性。
