Cairns S S, Bogenhagen D F
J Biol Chem. 1986 Jun 25;261(18):8481-7.
The mtDNA of the African frog, Xenopus laevis, has a triple-stranded displacement loop (D-loop) structure at the origin of heavy strand DNA replication. The major species of displacing strands has a length of 1670 nucleotides, approximately 3 times the length of mouse or human D-loop mtDNA strands. We report experiments that precisely map the termini of the D-loop strand within a revised sequence of the origin region. Analysis of D-loop mtDNA strands labeled in vitro at the 5' end using polynucleotide kinase and [gamma-32P]ATP reveals microheterogeneity at the 5' end. The ends detected by this technique are located in the vicinity of several matches to a sequence element, denoted CSB-1, that is conserved in this location in several vertebrate mtDNA genomes. The 3' ends of D-loop mtDNA strands labeled in vitro by limited extension with avian myeloblastosis virus reverse transcriptase and [gamma-32P] ATP are homogeneous. The sequence signals that may help specify the arrest of DNA replication at this site are discussed. The nucleotide sequence that we report for this region contains 53 discrepancies in comparison with a previously published sequence of this region of the Xenopus laevis mtDNA genome (Roe, B. A., Ma, D.-P., Wilson, R. K., and Wong, J.F.-H. (1985) J. Biol. Chem. 260, 9759-9774). Our sequence also contains a 142-nucleotide portion of the 5' end of the 12 S rRNA gene that was omitted from the sequence published by Roe et al.
非洲爪蟾（非洲爪蟾）的线粒体DNA（mtDNA）在重链DNA复制起点处具有三链置换环（D环）结构。置换链的主要种类长度为1670个核苷酸，约为小鼠或人类D环mtDNA链长度的3倍。我们报告了一些实验，这些实验在起始区域的修订序列中精确绘制了D环链的末端。使用多核苷酸激酶和[γ-32P]ATP在体外5'端标记的D环mtDNA链的分析揭示了5'端的微异质性。通过该技术检测到的末端位于与一个序列元件（称为CSB-1）的几个匹配序列附近，该序列元件在几个脊椎动物mtDNA基因组的这个位置是保守的。通过禽成髓细胞瘤病毒逆转录酶和[γ-32P]ATP的有限延伸在体外标记的D环mtDNA链的3'端是均匀的。讨论了可能有助于确定该位点DNA复制终止的序列信号。我们报告的该区域的核苷酸序列与之前发表的非洲爪蟾mtDNA基因组该区域的序列（Roe，B.A.，Ma，D.-P.，Wilson，R.K.和Wong，J.F.-H.（1985）J.Biol.Chem.260，9759-9774）相比有53个差异。我们的序列还包含12S rRNA基因5'端的142个核苷酸部分，这部分在Roe等人发表的序列中被遗漏了。
