GENE DEV:鈍性末端端粒亦可保護染色體末端

7月18日，GENE DEV雜誌在線報導，在被子植物中科學家發現不同於以往認識的鈍性末端端粒保護結構。

單鏈端粒DNA突出結構，被認為是進化上保守的基本結構元件，發揮保護染色體末端的重要功能。以前人們認為，此DNA突出結構在端粒部位的形成，由前導鏈機制複製導致。此過程涉及一種機制尚不清楚的DNA複製後鈍性末端處理。

出乎意料的是，本研究發現，被子植物包含鈍性末端和短的（1 - 3個核苷酸）包含G核苷的突出端粒結構，這些結構可穩定保留在有絲分裂後組織中。從而揭示了一種新的，保護染色體末端的機制。

平末端端粒的完整性取決於Ku70/80異二聚體，但不是在另一個端粒封蓋蛋白，STN1。奇怪的是，缺失Ku蛋白的端粒是功能完好的。這些端粒被核酸外切酶1切割，從而促進染色單體內重組，這可能有助於形成替代的染色體末端封蓋結構。

這些數據質疑這樣的觀點，即認為端粒需要單鏈DNA突起形成一個功能性的封蓋結構，並證明在染色體末端的保護問題上，大自然有著靈活的解決方案。（生物谷bioon.com）

Chromosome end protection by blunt-ended telomeres

Anita Kazda,Barbara Zellinger1,Max R?ssler1,Elisa Derboven1,Branislav Kusenda andKarel Riha

Single-stranded telomeric DNA protrusions are considered to be evolutionarily conserved structural elements essential for chromosome end protection. Their formation at telomeres replicated by the leading strand mechanism is thought to involve poorly understood post-replicative processing of blunt ends. Unexpectedly, we found that angiosperm plants contain blunt-ended and short (1- to 3-nucleotide) G-overhang-containing telomeres that are stably retained in post-mitotic tissues, revealing a novel mechanism of chromosome end protection. The integrity of blunt-ended telomeres depends on the Ku70/80 heterodimer but not on another telomere capping protein, STN1. Curiously, Ku-depleted telomeres are fully functional. They are resected by exonuclease 1, promoting intrachromatid recombination, which may facilitate formation of an alternative capping structure. These data challenge the view that telomeres require ssDNA protrusions for forming a functional capping structure and demonstrate flexibility in solutions to the chromosome end protection problem.