McCormick-Graham M, Haynes W J, Romero D P
Department of Pharmacology, Medical School, University of Minnesota, Minneapolis 55455, USA.
EMBO J. 1997 Jun 2;16(11):3233-42. doi: 10.1093/emboj/16.11.3233.
Telomeric DNA at the ends of chromosomes consist of short, tandem repeat sequences. The telomeres of Paramecium tetraurelia are made up of variable repeats, whereas Paramecium caudatum telomeric repeats are largely invariant. To investigate variable repeat synthesis in P. tetraurelia, mutated telomerase RNA genes were expressed in vivo. We demonstrate that the P. caudatum telomerase RNA can participate in telomere synthesis when expressed in the P. tetraurelia macronucleus, despite 24% primary sequence divergence of the RNAs between the two species. De novo telomeric repeats from transformants indicate that P. tetraurelia telomerase fidelity is dramatically affected by template substitutions and that misincorporation at a single templating position is likely to account for the majority of P. tetraurelia telomeric DNA variability. Furthermore, we show that fidelity is not solely a function of the RNA moiety, as the P. caudatum telomerase RNA does not impart high fidelity to the chimeric enzyme.
染色体末端的端粒DNA由短串联重复序列组成。四膜虫的端粒由可变重复序列构成，而尾草履虫的端粒重复序列在很大程度上是不变的。为了研究四膜虫中可变重复序列的合成，我们在体内表达了突变的端粒酶RNA基因。我们证明，尽管这两个物种的RNA一级序列有24%的差异，但尾草履虫的端粒酶RNA在四膜虫大核中表达时仍能参与端粒合成。转化体的新生端粒重复序列表明，四膜虫端粒酶的保真度受到模板替换的显著影响，单个模板位置的错误掺入可能是四膜虫端粒DNA变异的主要原因。此外，我们还表明，保真度不仅仅是RNA部分的功能，因为尾草履虫的端粒酶RNA不会赋予嵌合酶高保真度。
