replisome

Definition

Target type: cellularcomponent

A multi-component enzymatic machine at the replication fork which mediates DNA replication. Includes DNA primase, one or more DNA polymerases, DNA helicases, and other proteins. [GOC:mah, GOC:vw]

The replisome is a multi-protein complex responsible for DNA replication in all living organisms. It is a highly dynamic structure that assembles at the origin of replication and moves along the DNA strand, unwinding the double helix and synthesizing new DNA. The replisome consists of several core components, each with a specific role in the replication process.

**1. DNA Helicase:** This enzyme unwinds the DNA double helix, separating the two strands to expose the template strands for replication. In eukaryotes, the main replicative helicase is CMG (Cdc45-MCM-GINS). It is a ring-shaped complex that encircles the DNA and uses ATP hydrolysis to move along the strand.

**2. Single-Stranded DNA Binding Proteins (SSBs):** These proteins bind to the separated single strands of DNA, preventing them from re-annealing and protecting them from degradation. In eukaryotes, Replication Protein A (RPA) is the primary SSB.

**3. DNA Primase:** DNA primase is an RNA polymerase that synthesizes short RNA primers, which provide a starting point for DNA polymerase to begin DNA synthesis.

**4. DNA Polymerase:** DNA polymerases are the enzymes that synthesize new DNA strands using the template strands as guides. In eukaryotes, there are multiple DNA polymerases involved in replication. DNA polymerase α, a complex of four subunits, is responsible for initiating DNA synthesis and synthesizing short segments of DNA. DNA polymerase ε, a complex of four subunits, is responsible for replicating the leading strand, which is synthesized continuously. DNA polymerase δ, a complex of four subunits, is responsible for replicating the lagging strand, which is synthesized discontinuously in short fragments called Okazaki fragments.

**5. DNA Ligase:** DNA ligase joins the newly synthesized Okazaki fragments on the lagging strand to create a continuous DNA molecule.

**6. Topoisomerases:** Topoisomerases are enzymes that relieve the torsional stress that builds up in the DNA molecule as it is unwound by the helicase. They do this by cutting the DNA strands, allowing them to rotate, and then rejoining them.

**7. Sliding Clamp:** The sliding clamp is a ring-shaped protein that encircles the DNA and holds the DNA polymerase in place, allowing it to synthesize long stretches of DNA. In eukaryotes, PCNA is the primary sliding clamp.

**8. Clamp Loader:** The clamp loader is a protein complex that loads the sliding clamp onto the DNA. In eukaryotes, the RFC complex is the primary clamp loader.

These components interact in a complex and coordinated manner to ensure that DNA replication occurs accurately and efficiently. The replisome is a dynamic structure that can be assembled and disassembled as needed during the replication process. It is an essential component of all living organisms and is critical for the transmission of genetic information from one generation to the next.'
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Proteins (1)

Compounds (7)