DNA bending mediated by ORC is essential for replication licensing in budding yeast

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Eukaryotic DNA replication initiation relies on the origin recognition complex (ORC) and pre-replication complex (pre-RC).
• Replication licensing, mediated by ORC, involves assembling MCM2-7 complexes at origin DNA.

Purpose of the Study:

• To elucidate the role of the smallest ORC subunit, Orc6, in origin recognition and replication licensing.
• To investigate the structural mechanisms by which ORC binds and bends origin DNA.

Main Methods:

• Cryoelectron microscopy (cryo-EM) of yeast ORC mutants bound to origin DNA.
• Structural analysis of Orc6-DNA interactions and the Orc5 basic patch (BP).

Main Results:

• Orc6 uses its TFIIB-like domain to direct sequential ORC binding to DNA.
• Orc6 stabilizes Orc5-BP, enabling ORC to capture and bend origin DNA.
• Mutations disrupting Orc5-BP-mediated DNA bending significantly impair replication initiation.

Conclusions:

• Orc6 plays a critical, multifaceted role in orchestrating ORC-DNA interactions.
• DNA bending by ORC, facilitated by Orc6 and Orc5, is essential for efficient replication licensing.