Saveliev S V, Cox M M
Department of Biochemistry, University of Wisconsin-Madison, 433 Babcock Drive, Madison, WI 53706-1544, USA.
EMBO J. 2001 Jun 15;20(12):3251-61. doi: 10.1093/emboj/20.12.3251.
DNA sequences (IES elements) eliminated from the developing macronucleus in the ciliate Tetrahymena thermophila are released as linear fragments, which have now been detected and isolated. A PCR-mediated examination of fragment end structures reveals three types of strand scission events, reflecting three steps in the deletion process. New evidence is provided for two steps proposed previously: an initiating double-stranded cleavage, and strand transfer to create a branched deletion intermediate. The fragment ends provide evidence for a previously uncharacterized third step: the branched DNA strand is cleaved at one of several defined sites located within 15-16 nucleotides of the IES boundary, liberating the deleted DNA in a linear form.
在嗜热四膜虫发育中的大核中被消除的DNA序列(IES元件)以线性片段的形式释放出来,目前已被检测到并分离出来。通过PCR介导对片段末端结构的检测揭示了三种类型的链断裂事件,反映了缺失过程中的三个步骤。为之前提出的两个步骤提供了新证据:起始双链切割,以及形成分支缺失中间体的链转移。片段末端为之前未被描述的第三步提供了证据:分支DNA链在IES边界15 - 16个核苷酸内的几个特定位点之一被切割,以线性形式释放被删除的DNA。