Wang Lixin, Lin Chii Mei, Lopreiato Joseph O, Aladjem Mirit I
Laboratory of Molecular Pharmacology, National Cancer Institute, Bethesda, MD 20892, USA.
Hum Mol Genet. 2006 Sep 1;15(17):2613-22. doi: 10.1093/hmg/ddl187. Epub 2006 Jul 28.
The human beta globin locus contains two adjacent replicators, each capable of initiating DNA replication when transferred from its native locus to ectopic sites. Here, we report a detailed analysis of the sequence requirements for replication initiation from these replicators. In both replicators, initiation required a combination of an asymmetric purine:pyrimidine sequence and several AT-rich stretches. Modules from the two replicators could combine to initiate replication. AT-rich sequences were essential for replicator activity: a low frequency of initiation was observed in DNA fragments that included a short stretch of AT-rich sequences, whereas inclusion of additional AT-rich stretches increased initiation efficiency. By contrast, replication initiated at a low level without the asymmetric purine:pyrimidine modules but they were required in synergy to achieve efficient initiation. These data support a combinatorial model for replicator activity and suggest that the initiation of DNA replication requires interaction between at least two distinct sequence modules.
人类β珠蛋白基因座包含两个相邻的复制子，当从其天然基因座转移到异位位点时，每个复制子都能够启动DNA复制。在这里，我们报告了对这些复制子进行复制起始的序列要求的详细分析。在这两个复制子中，起始都需要不对称嘌呤：嘧啶序列和几个富含AT的片段的组合。来自两个复制子的模块可以组合起来启动复制。富含AT的序列对于复制子活性至关重要：在包含短的富含AT序列片段的DNA片段中观察到低频率的起始，而包含额外的富含AT的片段则提高了起始效率。相比之下，在没有不对称嘌呤：嘧啶模块的情况下，复制以低水平起始，但它们需要协同作用才能实现高效起始。这些数据支持复制子活性的组合模型，并表明DNA复制的起始需要至少两个不同序列模块之间的相互作用。
