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

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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.