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Published on: January 2, 2026
Orc2 protects ORCA from ubiquitin-mediated degradation
Zhen Shen1, Supriya G Prasanth
1Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
Cell Cycle (Georgetown, Tex.)
|September 1, 2012
Summary
Origin recognition complex-associated protein (ORCA) is degraded via ubiquitination at the G(1)/S phase boundary. Orc2 protein protects ORCA from this degradation, ensuring proper cell cycle progression.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- The Origin Recognition Complex (ORC) is crucial for DNA replication initiation.
- ORC subunits undergo cell cycle-dependent post-translational modifications.
- ORCA/LRWD1 stabilizes ORC and aids pre-RC assembly, with its levels varying across the cell cycle.
Purpose of the Study:
- To elucidate the mechanism regulating ORCA levels during the cell cycle.
- To investigate the role of ubiquitination in ORCA regulation.
- To identify proteins interacting with ORCA and influencing its stability.
Main Methods:
- In vivo ubiquitination assays to detect ORCA modification.
- Cell cycle analysis to correlate ubiquitination with cell cycle phases.
- Co-immunoprecipitation to identify interacting proteins, including E3 ligases.
- Western blotting to assess protein levels and ubiquitination status.
- Depletion studies (e.g., Orc2 depletion) to assess functional consequences.
Main Results:
- ORCA undergoes polyubiquitination in vivo, particularly at the G(1)/S boundary.
- Ubiquitination of ORCA involves Lysine-48 (K48) linkage, indicating proteasomal degradation.
- Ubiquitinated ORCA forms nuclear aggregates and associates with chromatin.
- ORCA interacts with the E3 ubiquitin ligase complex Cul4A-Ddb1.
- Ubiquitination occurs within the WD40 repeat domain, which is also recognized by Orc2.
- Orc2 binds to non-ubiquitinated ORCA; Orc2 depletion leads to ORCA destabilization via proteasome.
Conclusions:
- ORCA levels are regulated by ubiquitin-mediated degradation.
- The E3 ligase Cul4A-Ddb1 is involved in ORCA ubiquitination.
- Orc2 plays a protective role, preventing ORCA ubiquitination and degradation.
- This interaction between Orc2 and ORCA is critical for maintaining ORCA stability and potentially regulating DNA replication initiation.
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