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Primase (n.)
1.(MeSH)A single-stranded DNA-dependent RNA polymerase that functions to initiate, or prime, DNA synthesis by synthesizing oligoribonucleotide primers. EC 2.7.7.-.
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Primase (n.) [MeSH]
Wikipedia
DNA primase is an enzyme involved in the replication of DNA.
Primase catalyzes the synthesis of a short RNA (or DNA in some organisms [1]) segment called a primer complementary to a ssDNA template. Primase is of key importance in DNA replication because no known DNA polymerases can initiate the synthesis of a DNA strand without an initial RNA or DNA primer (for temporary DNA elongation).
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In bacteria, primase binds to the DNA helicase forming a complex called the primosome. Primase is activated by DNA helicase where it then synthesizes a short RNA primer approximately 11 ±1 nucleotides long, to which new nucleotides can be added by DNA polymerase.
The RNA segments are first elongated by DNA polymerase and then synthesized by primase.[2] Then the DNA polymerase forms a protein complex with two primase subunits to form the alpha DNA Polymerase primase complex. Primase is one of the most error prone and slow polymerases.[2] Primases in organisms such as E. coli, synthesize around 2000 to 3000 primers at the rate of one primer per second.[3] Primase also acts as a halting mechanism to prevent the leading strand from outpacing the lagging strand by halting the progression of the replication fork.[4] The rate determining step in primase is when the first phosphodiester bond is formed with the ssDNA.[2] The crystal structure of primase in E. coli with core that contained the DnaG protein was determined in 2000.[3] The DnaG and primase complex is cashew shaped and contains three subdomains.[3] The central subdomain forms a toprim fold which is made of a mixture five beta sheets and six alpha helices.[3] The toprim fold is used for binding regulators and metals. The primase uses a phosphotransfer domain for the transfer coordination of metals, which makes it distinct from other polymerases.[3] The side subunits contain a NH2 and COOH terminal made of alpha helixes and beta sheets.[3] The NH2 terminal interacts with a zinc binding domain and COOH-terminal region which interacts with DnaB-ID.[3] The replications mechanisms differ between different bacteria and viruses where the primase covalently link to helicase in viruses such as the T7 bacterialphage.[4] In viruses such as herpes simplex virus (HSV-1), primase can form complexes with helicase.[5] The primase-helicase complex is used to unwind dsDNA and synthesizes the lagging strand using RNA primers[5] The majority of primers synthesized by primase are two to three nucleotides long.[5]
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