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Eukaryotic DNA replication is a highly regulated process ensuring accurate genetic duplication. It involves specific proteins like DNA Polymerases α, ε, and δ, and the Cdc45–Mcm–GINS helicase complex, which unwinds DNA. The replication is coordinated by the proliferating cell nuclear antigen (PCNA) and regulated within the cell cycle, with mechanisms like telomerase addressing the end replication problem in linear chromosomes.
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Various proteins assemble at specific locations on the DNA to form a pre-replication complex
Synthesis of RNA Primer
Pol α, in complex with primase subunits PriS and PriL, synthesizes a short RNA primer necessary for DNA synthesis
Leading and Lagging Strand Synthesis
Pol α adds deoxyribonucleotides to the primer on the leading strand once at the origin and at the beginning of each Okazaki fragment on the lagging strand
Pol ε takes over on the leading strand, while Pol δ extends Okazaki fragments on the lagging strand, both with high processivity and proofreading capabilities
The Cdc45–Mcm–GINS (CMG) complex, consisting of Mcm2-7 helicase proteins, is pivotal in eukaryotic DNA replication, providing regulated helicase activity synchronized with DNA synthesis
The CMG complex becomes activated in the S phase, facilitating the unwinding of DNA at replication forks
The CMG complex, along with other regulatory factors, forms part of the Replisome Progression Complex, coordinating with DNA polymerases for efficient DNA synthesis
Ctf4 is essential for anchoring Polymerase α to replication origins, facilitating the initiation of DNA synthesis
Mrc1 and Claspin proteins link leading-strand synthesis with CMG helicase activity, ensuring coordinated and efficient replication fork progression
And1 protein associates with Polymerase α and the CMG complex, potentially playing a role in DNA replication
PCNA maintains a stable association between DNA polymerases and the DNA template during replication, enhancing processivity and facilitating recruitment of other replication proteins
Replication Factor C (RFC)
RFC uses ATP hydrolysis to load PCNA onto DNA and unload it upon completion of DNA synthesis, essential for the disassembly of the replication machinery
Sliding Clamp Mechanism
PCNA acts as a sliding platform, sliding along the DNA and recruiting various proteins at the replication fork for efficient DNA synthesis
Type II topoisomerases resolve interlinked daughter chromosomes in circular chromosomes
Telomeres and telomerase solve the end replication problem in linear chromosomes, preserving their stability and integrity
DNA replication is regulated within the cell cycle to ensure accurate and timely replication, essential for proper cell division and genomic integrity
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Origins of replication in eukaryotic DNA
Specific locations on DNA where replication begins; pre-replication complex forms here.
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Role of DNA Polymerase α (Pol α) in replication
Synthesizes short RNA primer with primase; starts DNA synthesis by adding deoxyribonucleotides.
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Function of DNA Polymerase ε (Pol ε)
Takes over synthesis on leading strand after Pol α; has high processivity and proofreading.
