Molecular basis for telomere repeat divergence in budding yeast
Molecular basis for telomere repeat divergence in budding yeast
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DOI：
10.1128/mcb.21.21.7277-7286.2001
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发表时间：
2001-11-01
影响因子：
5.3
通讯作者：
Lingner, J
中科院分区：
文献类型：
--
作者：
Förstemann, K;Lingner, J
端粒酶是一种核糖核蛋白酶，它将重复序列添加到线性染色体的末端，从而抵消由于不完全复制而导致的核苷酸损失。端粒酶RNA亚基的短区域作为核苷酸添加到端粒3'端的模板。虽然酿酒酵母只含有一个端粒酶RNA基因，但端粒重复序列在这种生物中是退化的。通过对野生型和突变型RNA模板在体内指定的端粒序列的详细分析，我们发现端粒重复序列的差异是由于模板3‘和5’区域的逆转录失败以及RNA模板内多个寄存器的端粒排列。通过对野生型端粒序列的解释，我们确定了模板中在底物退火过程中无法进行碱基配对的核苷酸。相反，这些位置只有在与相邻核苷酸对齐后才能成为逆转录的模板，这表明在底物结合时发生了构象变化。我们还推断，模板区的中心部分是逆转录的过程。某些模板位置的不可接近性和中心模板部分的过程聚合可能有助于减少可能的重复多样化，并增强Rap1p结合位点的结合，Rap1p是出芽酵母的端粒结合蛋白。
Telomerase is a ribonucleoprotein enzyme that adds repetitive sequences to the ends of linear chromosomes, thereby counteracting nucleotide loss due to incomplete replication. A short region of the telomerase RNA subunit serves as template for nucleotide addition onto the telomere 3' end. Although Saccharomyces cerevisiae contains only one telomerase RNA gene, telomere repeat sequences are degenerate in this organism. Based on a detailed analysis of the telomere sequences specified by wild-type and mutant RNA templates in vivo, we show that the divergence of telomere repeats is due to abortive reverse transcription in the 3' and 5' regions of the template and due to the alignment of telomeres in multiple registers within the RNA template. Through the interpretation of wild-type telomere sequences, we identify nucleotides in the template that are not accessible for base pairing during substrate annealing. Rather, these positions become available as templates for reverse transcription only after alignment with adjacent nucleotides has occurred, indicating that a conformational change takes place upon substrate binding. We also infer that the central part of the template region is reverse transcribed processively. The inaccessibility of certain template positions for alignment and the processive polymerization of the central template portion may serve to reduce the possible repeat diversification and enhance the incorporation of binding sites for Rap1p, the telomere binding protein of budding yeast.