Orc2 protects ORCA from ubiquitin-mediated degradation
Origin recognition complex (ORC) is highly dynamic, with several ORC subunits getting posttranslationally modified by phosphorylation or ubiquitination in a cell cycle-dependent manner. We have previously demonstrated that a WD repeat containing protein ORC-associated (ORCA/LRWD1) stabilizes the ORC...
| Published in: | Cell Cycle |
|---|---|
| Main Authors: | , |
| Format: | Text |
| Language: | English |
| Published: |
Landes Bioscience
2012
|
| Subjects: | |
| Online Access: | http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3478309 http://www.ncbi.nlm.nih.gov/pubmed/22935713 https://doi.org/10.4161/cc.21870 |
| Summary: | Origin recognition complex (ORC) is highly dynamic, with several ORC subunits getting posttranslationally modified by phosphorylation or ubiquitination in a cell cycle-dependent manner. We have previously demonstrated that a WD repeat containing protein ORC-associated (ORCA/LRWD1) stabilizes the ORC on chromatin and facilitates pre-RC assembly. Further, ORCA levels are cell cycle-regulated, with highest levels during G1, and progressively decreasing during S phase, but the mechanism remains to be elucidated. We now demonstrate that ORCA is polyubiquitinated in vivo, with elevated ubiquitination observed at the G1/S boundary. ORCA utilizes lysine-48 (K48) ubiquitin linkage, suggesting that ORCA ubiquitination mediates its regulated degradation. Ubiquitinated ORCA is re-localized in the form of nuclear aggregates and is predominantly associated with chromatin. We demonstrate that ORCA associates with the E3 ubiquitin ligase Cul4A-Ddb1. ORCA is ubiquitinated at the WD40 repeat domain, a region that is also recognized by Orc2. Furthermore, Orc2 associates only with the non-ubiquitinated form of ORCA, and Orc2 depletion results in the proteasome-mediated destabilization of ORCA. Based on the results, we suggest that Orc2 protects ORCA from ubiquitin-mediated degradation in vivo. |
|---|