Samadashwily G M, Dayn A, Mirkin S M
Department of Genetics, University of Illinois at Chicago 60612.
EMBO J. 1993 Dec 15;12(13):4975-83. doi: 10.1002/j.1460-2075.1993.tb06191.x.
Studying the activity of T7 DNA polymerase (Sequenase) on open circular DNAs, we observed virtually complete termination within potential triplex-forming sequences. Mutations destroying the triplex potential of the sequences prevented termination, while compensatory mutations restoring triplex potential restored it. We hypothesize that strand displacement during DNA polymerization of double-helical templates brings three DNA strands (duplex DNA downstream of the polymerase plus a displaced overhang) into close proximity, provoking triplex formation, which in turn prevents further DNA synthesis. Supporting this idea, we found that Sequenase is unable to propagate through short triple-helical stretches within single-stranded DNA templates. Thus, DNA polymerase, by inducing triplex formation at specific sequences in front of the replication fork, causes self-termination. Possible biological implications of such 'conformational suicide' are discussed. Our data also provide a novel way to target DNA polymerases at specific sequences using triplex-forming oligonucleotides.
在研究T7 DNA聚合酶（测序酶）对开环DNA的活性时，我们观察到在潜在的三链体形成序列内几乎完全终止。破坏这些序列三链体形成潜力的突变可阻止终止，而恢复三链体形成潜力的补偿性突变则可恢复终止。我们推测，在双链模板的DNA聚合过程中链置换会使三条DNA链（聚合酶下游的双链DNA加上一条被置换的突出端）紧密靠近，引发三链体形成，进而阻止进一步的DNA合成。支持这一观点的是，我们发现测序酶无法穿过单链DNA模板内的短三链体片段。因此，DNA聚合酶通过在复制叉前方的特定序列处诱导三链体形成而导致自我终止。本文讨论了这种“构象自杀”可能的生物学意义。我们的数据还提供了一种使用三链体形成寡核苷酸在特定序列处靶向DNA聚合酶的新方法。
