The ORC ubiquitin ligase OBI1 promotes DNA replication origin firing

• Published in: Nature communications 2019-06, Vol.10 (1), p.2426-2426, Article 2426
• Main Authors: Coulombe, Philippe, Nassar, Joelle, Peiffer, Isabelle, Stanojcic, Slavica, Sterkers, Yvon, Delamarre, Axel, Bocquet, Stéphane, Méchali, Marcel
• Format: Article
• Language: English
• Subjects: 13; 38; 631/337/151/2352; 631/337/151/2355; Cdc45 protein; Cell cycle; Chromatin; Complex formation; Deoxyribonucleic acid; DNA; DNA biosynthesis; DNA Replication - physiology; Firing; G1 Phase - physiology; Genetics; Humanities and Social Sciences; Humans; Kinases; Life Sciences; multidisciplinary; Mutants; Origin Recognition Complex - genetics; Origin Recognition Complex - metabolism; Origins; Proteomics; Replication; Replication initiation; Replication Origin - physiology; Replication origins; S Phase - physiology; Science; Science (multidisciplinary); Signal transduction; Substrates; Ubiquitin; Ubiquitin-protein ligase; Ubiquitin-Protein Ligases - genetics; Ubiquitin-Protein Ligases - metabolism; Ubiquitination
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-019-10321-x

DNA replication initiation is a two-step process. During the G1-phase of the cell cycle, the ORC complex, CDC6, CDT1, and MCM2–7 assemble at replication origins, forming pre-replicative complexes (pre-RCs). In S-phase, kinase activities allow fork establishment through (CDC45/MCM2–7/GINS) CMG-complex formation. However, only a subset of all potential origins becomes activated, through a poorly understood selection mechanism. Here we analyse the pre-RC proteomic interactome in human cells and find C13ORF7/RNF219 (hereafter called OBI1, for ORC-ubiquitin-ligase-1) associated with the ORC complex. OBI1 silencing result in defective origin firing, as shown by reduced CMG formation, without affecting pre-RC establishment. OBI1 catalyses the multi-mono-ubiquitylation of a subset of chromatin-bound ORC3 and ORC5 during S-phase. Importantly, expression of non-ubiquitylable ORC3/5 mutants impairs origin firing, demonstrating their relevance as OBI1 substrates for origin firing. Our results identify a ubiquitin signalling pathway involved in origin activation and provide a candidate protein for selecting the origins to be fired. DNA replication is initiated at defined genomic sites called origins of replication following ORC pre-replicative complex assembly. Here the authors identify a protein ubiquitylating ORC that is involved in origin activation and may act as a selector of origins to be fired.