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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.
In molecular biology, a primosome is a protein complex responsible for creating RNA primers on single stranded DNA during DNA replication. The primosome consists of seven proteins: DnaG primase, DnaB helicase, DnaC helicase assistant, DnaT, PriA, Pri B, and PriC.
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.
This primase is structurally similar to many viral RNA-dependent RNA polymerases, reverse transcriptases, cyclic nucleotide generating cyclases and DNA polymerases of the A/B/Y families that are involved in DNA replication and repair. In eukaryotic replication, the primase forms a complex with Pol α. [35]
DNA primase small subunit is an enzyme that in humans is encoded by the PRIM1 gene. [ 5 ] The replication of DNA in eukaryotic cells is carried out by a complex chromosomal replication apparatus, in which DNA polymerase alpha and primase are two key enzymatic components.
The use of RdRp plays a major role in RNA interference in eukaryotes, a process used to silence gene expression via small interfering RNAs binding to mRNA rendering them inactive. [36] Eukaryotic RdRp becomes active in the presence of dsRNA, and is less widely distributed than other RNAi components as it lost in some animals, though still found ...
However, primase creates RNA primers at a much lower rate than that at which DNA polymerase synthesizes DNA on the leading strand. DNA polymerase on the lagging strand also has to be continually recycled to construct Okazaki fragments following RNA primers. This makes the speed of lagging strand synthesis much lower than that of the leading strand.
The most prominent examples of RNA genes are transfer RNA (tRNA) and ribosomal RNA (rRNA), both of which are involved in the process of translation. However, since the late 1990s, many new RNA genes have been found, and thus RNA genes may play a much more significant role than previously thought.