The origin recognition complex requires chromatin tethering by a hypervariable intrinsically disordered region that...

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Eukaryotic genome duplication requires loading the replicative helicase onto chromatin.
• This process, known as 'licensing,' begins with the origin recognition complex (ORC) recruiting to chromatin.
• ORC recruitment was previously thought to depend on ATP-dependent DNA binding and encirclement.

Purpose of the Study:

• To investigate the mechanism of metazoan ORC chromatin binding.
• To determine the role of the intrinsically disordered region (IDR) of Orc1 in ORC recruitment.
• To explore the evolutionary conservation of Orc1 IDRs.

Main Methods:

• In vivo recruitment assays using fly ORC.
• In vitro DNA binding assays.
• Phylogenetic analysis of metazoan Orc1 IDRs.

Main Results:

• The intrinsically disordered region (IDR) of fly Orc1 is necessary and sufficient for ORC recruitment to chromosomes.
• IDR phosphorylation regulates ORC recruitment.
• The IDR confers ATP-independent DNA binding activity to the ORC holocomplex.
• Metazoan Orc1 IDRs are functionally conserved despite significant sequence divergence.

Conclusions:

• Metazoan ORC chromatin binding is mediated by an IDR-dependent tethering mechanism, not solely ATP-dependent activity.
• This IDR-mediated tethering is essential for initiating eukaryotic genome duplication.
• The functional conservation of divergent Orc1 IDRs highlights an adaptable evolutionary strategy for essential cellular processes.