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The Biochemistry of Initiating Eukaryotic DNA Replication

The origin recognition complex (ORC) was initially discovered in budding yeast extracts as a protein complex that binds to the autonomously replicating sequence (ARS) to initiate DNA replication. Human homologues of the six ORC subunits have been identified and have been shown to play an important role in eukaryotic DNA replication as well. In this Paper of the Week, Khalid Siddiqui and Bruce Stillman examined the biochemical reactions required for the formation of this complex in eukaryotes.

The ORC complex is assembled in an ATP-dependent manner during G1.

The researchers reconstituted the human ORC using a baculovirus expression system and showed that ATP is essential for human ORC assembly in vitro. They also examined complex formation, the role of ATP binding in complex assembly, and the association of the subunits across the cell cycle. From their results, they suggest that the assembly and disassembly of ORC in human cells is uniquely regulated and may contribute to restricting DNA replication to once in every cell division cycle.

FOOTNOTES

See referenced article, J. Biol. Chem. 2007, 282, 32370-32383

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