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DNA primase is an enzyme involved in the replication of DNA and is a type of RNA polymerase. Primase catalyzes the synthesis of a short RNA (or DNA in some living organisms [ 1 ] ) segment called a primer complementary to a ssDNA (single-stranded DNA) template.
The E. Coli DnaG primase is a 581 residue monomeric protein with three functional domains, according to proteolysis studies. There is an N-terminal Zinc-binding domain (residues 1–110) where a zinc ion is tetrahedrally coordinated between one histidine and three cysteine residues, which plays a role in recognizing sequence specific DNA binding sites.
The structure of the DNA double helix (type B-DNA). The atoms in the structure are color-coded by element and the detailed structures of two base pairs are shown in the bottom right. DNA exists as a double-stranded structure, with both strands coiled together to form the characteristic double helix.
(b) The polymerase alpha–primase synthesizes a short RNA–DNA primer in the 5' to 3' direction, displacing RPA molecules as it travels along the template. (c) Following completion of the primer, the clamp loader displaces polymerase alpha and catalyzes loading of the sliding clamp and DNA polymerase delta or epsilon.
DNA polymerase III synthesizes base pairs at a rate of around 1000 nucleotides per second. [3] DNA Pol III activity begins after strand separation at the origin of replication. Because DNA synthesis cannot start de novo, an RNA primer, complementary to part of the single-stranded DNA, is synthesized by primase (an RNA polymerase): [citation ...
T7 DNA helicase (gp4) is a hexameric motor protein encoded by T7 phages that uses energy from dTTP hydrolysis to process unidirectionally along single stranded DNA, separating the two strands as it progresses. It is also a primase, making short stretches of RNA that initiates DNA synthesis. [2] It forms a complex with T7 DNA polymerase.
Not only is the general topology conserved, the two also share a bifunctional primase-and-PCNA-binding PIP-box sequence on the C-terminus, similar to both eukaryotic Polα and Polε. [37] In 1998, the family D of DNA polymerase was discovered in Pyrococcus furiosus and Methanococcus jannaschii. [38]
Helicase is an enzyme which breaks hydrogen bonds between the base pairs in the middle of the DNA duplex. Its doughnut like structure wraps around DNA and separates the strands ahead of DNA synthesis. In eukaryotes, the Mcm2-7 complex acts as a helicase, though which subunits are required for helicase activity is not entirely clear. [2]