Maric Chrystelle, Bénard Marianne, Pierron Gérard
Laboratoire Réplication de l'ADN et Ultrastructure du Noyau, CNRS-FRE 3238, Institut André Lwoff, 7 rue Guy Môquet, BP 8, 94801, Villejuif Cedex, France.
Chromosoma. 2010 Dec;119(6):601-11. doi: 10.1007/s00412-010-0281-x. Epub 2010 Jul 7.
Transient four stranded joint DNA molecules bridging sister chromatids constitute an intriguing feature of replicating genomes. Here, we studied their structure and frequency of formation in Physarum polycephalum. By "3D gels", we evidenced that they are not made of four continuous DNA strands. Discontinuities, which do not interfere with the unique propensity of the joint DNA molecules to branch migrate in vitro, are linked to the crossover, enhanced by RNaseA, and affect at most half of the DNA strands. We propose a structural model of joint DNA molecules containing ribonucleotides inserted within one strand, a gapped strand, and two continuous DNA strands. We further show that spontaneous joint DNA molecules are short-lived and are as abundant as replication forks. Our results emphasize the highly frequent formation of joint DNA molecules involving newly replicated DNA in an untreated cell and uncover a transitory mechanism connecting the sister chromatids during S phase.
短暂存在的连接姐妹染色单体的四链节DNA分子构成了复制基因组的一个有趣特征。在此，我们研究了它们在多头绒泡菌中的结构和形成频率。通过“三维凝胶”，我们证明它们并非由四条连续的DNA链组成。这些不连续性并不干扰连接DNA分子在体外分支迁移的独特倾向，它们与交叉有关，经核糖核酸酶A增强，并且最多影响一半的DNA链。我们提出了一种连接DNA分子的结构模型，该模型包含一条链内插入核糖核苷酸的、有缺口的链以及两条连续的DNA链。我们进一步表明，自发形成的连接DNA分子寿命短暂，且与复制叉数量相当。我们的结果强调了在未处理细胞中涉及新复制DNA的连接DNA分子的高频形成，并揭示了在S期连接姐妹染色单体的一种短暂机制。
