Adam R D, Nash T E, Wellems T E
Department of Internal Medicine, University of Arizona, Tucson 85724.
Mol Cell Biol. 1991 Jun;11(6):3326-30. doi: 10.1128/mcb.11.6.3326-3330.1991.
Giardia lamblia telomeres have been isolated from a library enriched for repaired chromosome ends by (i) screening with a Plasmodium falciparum telomere and (ii) differential hybridization with Bal 31-digested and total G. lamblia DNA. Analysis of three clones isolated by this strategy has identified multiple tandem repeats of the 5-mer TAGGG. An oligonucleotide containing these repeats recognizes Bal 31-sensitive bands in Southern hybridizations and detects all G. lamblia chromosomes in pulsed-field gel electrophoresis separations. An abrupt transition from the G. lamblia rDNA sequence to telomeric repeats has been found in all three clones. In two of the clones the transition occurs at the same site, near the beginning of the large subunit rDNA sequence. In the third clone the transition occurs at a site in the intergenic spacer sequence between the rDNA genes. Hybridization of an rDNA probe to a pulsed-field separation of G. lamblia chromosomes indicates that rDNA genes are present on several chromosomes but vary in location from isolate to isolate. These results suggest that rRNA genes are clustered at telomeric locations in G. lamblia and that these clusters are mobile.
（i）用恶性疟原虫端粒进行筛选，以及（ii）与经Bal 31消化的蓝氏贾第鞭毛虫DNA和总蓝氏贾第鞭毛虫DNA进行差异杂交。对通过该策略分离出的三个克隆进行分析，确定了5聚体TAGGG的多个串联重复序列。含有这些重复序列的寡核苷酸在Southern杂交中识别对Bal 31敏感的条带，并在脉冲场凝胶电泳分离中检测到所有蓝氏贾第鞭毛虫染色体。在所有三个克隆中都发现了从蓝氏贾第鞭毛虫rDNA序列到端粒重复序列的突然转变。在其中两个克隆中，转变发生在同一位置，靠近大亚基rDNA序列的起始处。在第三个克隆中，转变发生在rDNA基因之间的基因间隔序列中的一个位点。用rDNA探针与蓝氏贾第鞭毛虫染色体的脉冲场分离物杂交表明，rDNA基因存在于几条染色体上，但不同分离株的位置有所不同。这些结果表明，rRNA基因在蓝氏贾第鞭毛虫中聚集在端粒位置，并且这些簇是可移动的。
