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Hum Mol Genet. 2006 Sep 1;15(17):2613-22. Epub 2006 Jul 28.

Cooperative sequence modules determine replication initiation sites at the human beta-globin locus.

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Laboratory of Molecular Pharmacology, National Cancer Institute, Bethesda, MD 20892, USA.


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.

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