The function and role of telomeric palindrom sequence newly found in tobacco chromosomes

DNA的增加和基因组的线性化（染色体的形成）是真核生物在进化过程中分化的根本基础。端粒和端粒酶是真核生物线状染色体不可缺少的组成部分。不幸的是，人们对植物端粒的分子结构知之甚少。在本研究项目中，我们在烟草染色体中发现并测序了新的RETS（限制性内切酶抗性高分子量端粒DNA序列）。利用RETS作为探针，我们对烟草染色体末端的结构进行了表征。此外，Southern分析清楚地表明RETS分布在烟草染色体上。根据这些结果，我们提出了一个工作假设，即RETS为染色体损伤修复中的端粒形成提供了种子。为了了解端粒的功能，我们构建了首个可移动的酵母人工染色体YAC (yeast artificial chromosome)，其中oriT （origin of transfer）被插入到两个端粒之间。利用辅助质粒上的mob（动员）和tra（转移）基因，成功地将该质粒从大肠杆菌转移到酿酒酵母中。然而，尽管在跨界结合过程中端粒之间的OriT被切割，但跨界接合酵母的YACs不是线性的，而是圆形的。这表明线性化的YAC的5'端可能被偶联管中类似暴徒蛋白片段的物质阻断或锚定。

The increasing DNA and linearlization of genomes (chromosome formation) are fundamental basis for divergence of eukaryotes from prokaryotes during evolution. The telomeres and telomerase are indispensable for eukaryotic linear chromosomes. Unfortunately, little is known the molecular structure of telomeres in plants. In this research project, we have found and sequenced novel RETS (restriction enzymes-resistant high molecular weight telomeric DNA sequences) in tabacco chromosomes. By using RETS as a probe, we characterized the terminal structure of tobacco chromosomal ends. Furthermore, Southern analysis clearly indicates that RETS are spread out all over the tobacco chromosomes. From these results, we have presented a working hypothesis that RETS offer a seed for telomere formation in the repair of chromosomal damages. In order to know functions of telomere, we constructed the first mobilizable YAC (yeast artificial chromosome) in which oriT (origin of transfer) is inserted between two telomeres. This plasmid was successfully transferred from Escherichia coli bacterium into Saccharomyces cerevisae yeast with the help of mob (mobilization) and tra (transfer) genes on a helper plasmid. However, the transconjugant yeasts had not linear YACs but circular YACs although OriT between telomeres was nicked during trans-kingdom conjugation. This indicates that 5'end of linearlized YAC might be blocked or anchored by something like mob protein moiety which locates in a conjugation tube.