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Primase is a RNA polymerase which is responsible for the synthesis for a short piece of RNA which is then able to act as a primer in DNA synthesis. The synthesised RNA primer is very small in size (approximately 4 nucleotides long) and synthesis of the primer can be initiated without the presence of another primer. In E.coli the primase is DnaG, the product of the DnaG gene. The primer is complementary to a section of DNA and hence binds to it, thus allowing DNA polymerase III to initiate synthesis of new DNA in the 5' to 3' direction. At a later stage of DNA synthesis the primer is removed and replaced by DNA (for example this is done on the lagging strand of DNA by DNA polymerase I which contains an exonuclease enzyme)[1].


  1. Berg J.M., Tymoczko J.L., Styer L. (2012) Biochemistry, 7th edition, New York, W.H Freeman.
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