Sogo J M, Stahl H, Koller T, Knippers R
J Mol Biol. 1986 May 5;189(1):189-204. doi: 10.1016/0022-2836(86)90390-6.
The structure of replicating simian virus 40 (SV40) minichromosomes was studied by DNA crosslinking with trimethyl-psoralen. The procedure was used both in vitro with extracted SV40 minichromosomes as well as in vivo with SV40-infected cells. Both procedures gave essentially the same results. Mature SV40 minichromosomes are estimated to contain about 27 nucleosomes (error +/- 2), except for those molecules with a nucleosome-free gap, which are interpreted to contain 25 nucleosomes (error +/- 2). In replicative intermediates, nucleosomes are present in the unreplicated parental stem with the replication fork possibly penetrating into the nucleosomal DNA before the histone octamer is removed. Nucleosomes reassociate on the newly replicated DNA branches at distances from the branch point of 225 ( +/- 145) nucleotides on the leading strand and of 285( +/- 120) nucleotides on the lagging strand. In the presence of cycloheximide, daughter duplexes contained unequal numbers of nucleosomes, supporting dispersive and random segregation of parental nucleosomes. These were arranged in clusters with normal nucleosome spacing. We detected a novel type of interlocked dimer comprising two fully replicated molecules connected by a single-stranded DNA bridge. We cannot decide whether these dimers represent hemicatenanes or whether the two circles are joined by a Holliday-type structure. The joining site maps within the replication terminus. We propose that these dimers represent molecules engaged in strand segregation.
通过用三甲基补骨脂素进行DNA交联，研究了复制型猿猴病毒40（SV40）微型染色体的结构。该方法既用于体外提取的SV40微型染色体，也用于体内感染SV40的细胞。两种方法得到的结果基本相同。估计成熟的SV40微型染色体含有约27个核小体（误差±2），但那些有无核小体间隙的分子被解释为含有25个核小体（误差±2）。在复制中间体中，核小体存在于未复制的亲本主干中，复制叉可能在组蛋白八聚体被去除之前穿透到核小体DNA中。核小体在新复制的DNA分支上重新结合，在前导链上距离分支点225（±145）个核苷酸处，在滞后链上距离分支点285（±120）个核苷酸处。在放线菌酮存在的情况下，子代双链体含有不等数量的核小体，支持亲本核小体的分散和随机分离。这些核小体以正常的核小体间距成簇排列。我们检测到一种新型的互锁二聚体，它由两个通过单链DNA桥连接的完全复制的分子组成。我们无法确定这些二聚体是代表半连环体，还是两个环通过霍利迪型结构连接。连接位点定位在复制末端内。我们提出这些二聚体代表参与链分离的分子。
