![]() coli enzyme now known as DNA polymerase I or Pol I, was discovered and characterized in 1957 by Arthur Kornberg (who received the Nobel prize for this work). However primase, as can all RNA polymerases, does not require a primer to initiate polynucleotide synthesis it can do so by linking together two NTPs in a 3' → 5' linkage. This enzyme catalyzes a reaction similar to that catalyzed by DNA polymerase but uses NTPs rather than dNTPs. If DNA polymerase can only add nucleotides to a pre-existing primer strand, how can the primer be synthesized? The answer is that the initial primer is a short RNA strand that is complementary to the a portion of the template strand and which is synthesized by an RNA polymerase known as primase. ![]() In addition, DNA polymerases cannot initiate replication by linking together two dNTPs, but rather, can only link the incoming nucleotide to a terminal 3'-OH group on an existing polynucleotide strand, the so-called primer strand, thereby forming a 3' → 5' phosphodiester bond between successive deoxynucleotides. DNA polymerases catalyze the reaction (DNA) n residues + dNTP → (DNA) n+1 residues + PP i, where dNTP is the deoxynucleoside triphosphate whose base is complementary to a base on the strand being copied, the so-called template strand. All cells express several different DNA polymerases that variously participate in the several aspects of DNA replication and in the repair of damaged DNA. DNA replication is catalyzed by DNA polymerase.
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