A Link between ORC-Origin Binding Mechanisms and Origin Activation Time Revealed in Budding Yeast: e1003798

• Published in: PLoS genetics 2013-09, Vol.9 (9)
• Main Authors: Hoggard, Timothy, Shor, Erika, Müller, Carolin A, Nieduszynski, Conrad A, Fox, Catherine A
• Format: Article
• Language: English
• Subjects: Cell cycle; Chromosomes; Deoxyribonucleic acid; DNA; Studies; Yeast
• ISSN: 1553-7390; 1553-7404
• DOI: 10.1371/journal.pgen.1003798

Eukaryotic DNA replication origins are selected in G1-phase when the origin recognition complex (ORC) binds chromosomal positions and triggers molecular events culminating in the initiation of DNA replication (a.k.a. origin firing) during S-phase. Each chromosome uses multiple origins for its duplication, and each origin fires at a characteristic time during S-phase, creating a cell-type specific genome replication pattern relevant to differentiation and genome stability. It is unclear whether ORC-origin interactions are relevant to origin activation time. We applied a novel genome-wide strategy to classify origins in the model eukaryote Saccharomyces cerevisiae based on the types of molecular interactions used for ORC-origin binding. Specifically, origins were classified as DNA-dependent when the strength of ORC-origin binding in vivo could be explained by the affinity of ORC for origin DNA in vitro, and, conversely, as 'chromatin-dependent' when the ORC-DNA interaction in vitro was insufficient to explain the strength of ORC-origin binding in vivo. These two origin classes differed in terms of nucleosome architecture and dependence on origin-flanking sequences in plasmid replication assays, consistent with local features of chromatin promoting ORC binding at 'chromatin-dependent' origins. Finally, the 'chromatin-dependent' class was enriched for origins that fire early in S-phase, while the DNA-dependent class was enriched for later firing origins. Conversely, the latest firing origins showed a positive association with the ORC-origin DNA paradigm for normal levels of ORC binding, whereas the earliest firing origins did not. These data reveal a novel association between ORC-origin binding mechanisms and the regulation of origin activation time.