Origins of DNA Replication in Eukaryotic Cells

Eukaryotic chromosomes replicate from multiple discrete loci termed origins of replication. These sites are first recognised by the origin recognition complex (ORC), which, together with Cdc6 and Cdt1, loads the inactive replicative helicase, MCM2–7, to form a pre-replicative complex (pre-RC) during G1 phase. Upon entry into S phase, cyclin-dependent kinases and Dbf4-dependent kinase phosphorylate key factors, triggering helicase activation and bidirectional fork establishment. Origins differ in sequence composition, chromatin environment and epigenetic marks, resulting in temporally regulated firing across replication timing domains. Yeast models have defined minimal replicator elements, whereas metazoan origins are more plastic and influenced by nucleosome positioning, transcriptional activity and three-dimensional genome architecture. Proper origin selection and activation ensure complete and accurate genome duplication; failure to regulate origin usage contributes to replication stress, genome instability and disease, while differential origin usage underpins development and cell-type specificity.

Research from Nature Portfolio

Recent studies have employed single-cell sequencing to map origin activation with unprecedented resolution, revealing cell-to-cell variability in origin usage and linking differential firing to local chromatin accessibility. Structural investigations using cryo-electron microscopy have captured the ORC–Cdc6–Cdt1–MCM2–7 assembly in distinct conformational states, elucidating the molecular basis of helicase loading and its regulation by origin-associated kinases. Another report has identified non-canonical DNA structures, specifically G-quadruplex motifs, within early-firing origins in mammalian genomes, demonstrating that these elements enhance ORC binding and coordinate replication timing programmes with transcriptional landscapes.

Origins of DNA Replication in Eukaryotic Cells publication trend

The graph below shows the total number of articles in origins of dna replication in eukaryotic cells across all publications each year (not limited to Nature Index journals).

Technical terms

Origin of replication: A genomic locus where DNA synthesis is initiated bidirectionally.

Origin recognition complex (ORC): A six-subunit protein assembly that binds replicator DNA to nucleate pre-RC formation.

Licensing: The process of loading inactive MCM2–7 helicase onto origins during G1 phase.

MCM2–7 complex: The hexameric replicative helicase responsible for unwinding DNA at replication forks.

Origin firing: Activation of licensed origins through kinase-mediated phosphorylation, leading to helicase unwinding.

Replicon: The DNA region replicated from a single origin of replication.

G-quadruplex: A four-stranded DNA secondary structure formed by stacked guanine tetrads, implicated in origin efficiency.

Replication stress: Conditions that impede fork progression or origin activation, risking genomic instability.

References

1. Emetine blocks DNA replication via proteosynthesis inhibition not by targeting Okazaki fragments. Life Science Alliance (2022).
2. Mimosine Arrests DNA Synthesis at Replication Forks by Inhibiting Deoxyribonucleotide Metabolism (∗). Journal of Biological Chemistry (1995).
3. Recent advances in the genome-wide study of DNA replication origins in yeast. Frontiers in Microbiology (2015).
4. Noncanonical DNA Elements in the Lamin B2 Origin of DNA Replication*. Journal of Biological Chemistry (2004).