10 Difference Between DNA Polymerase 1 And 3

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DNA Polymerase I (Pol I)

DNA polymerase I (or Pol I) is an enzyme that participates in the process of prokaryotic DNA replication. Discovered by Arthur Kornberg in 1956, it was the first known DNA polymerase (and the first known of any kind of polymerase). It was initially characterized in E. coli and is ubiquitous in prokaryotes.

In E. coli and many other bacteria, the gene that encodes Pol I is known as polA. Escherichia coli DNA polymerase I, the first DNA polymerase to be discovered and also the first to be studied structurally, serves as an important prototype for this family of enzymes.

The E. coli form of the enzyme is composed of 928 amino acids, and is an example of a processive enzyme—it can sequentially catalyze multiple polymerisations without releasing the single-stranded template. The physiological function of Pol I is mainly to repair any damage with DNA, but it also serves to connect Okazaki fragments by deleting RNA primers and replacing the strand with DNA.

The bacterial DNA polymerase I enzymes are multifunctional, with three distinct enzymatic activities located on three separate structural domains. In addition to the polymerase activity, there is a 3′–5′ exonuclease that serves to proofread polymerase errors, and a structure-specific 5′ nuclease capable of removing a DNA strand ahead of the site of polymerase addition during synthesis on double-stranded DNA.

All three enzymatic activities involve phosphoryl transfer reactions and are dependent on divalent metal ions, bound via carboxylate ligands at each active site. Extensive kinetic studies, together with co-crystal structures of DNA polymerases with bound substrates, have contributed to our understanding of the polymerase reaction pathway. The chemical step of nucleotide addition is preceded by several conformational transitions which contribute to the exquisite specificity and low error rate of DNA polymerases.

What You Need To Know About DNA Polymerase I

  • DNA polymerase I also referred to as Pol I, manly functions to synthesize short stretches of DNA during excision repair and to remove RNA primers and fill the gaps between Okazaki fragments in lagging strand replication.
  • It was discovered by Arthur Kornberg in 1956.
  • DNA polymerase 1 is encoded by polyA gene.
  • It belongs to the DNA polymerase family A.
  • DNA polymerase removes the RNA primer.
  • It has both 3’ to 5’ exonuclease activity and 5’ to 3’ exonuclease activity.
  • DNA polymerase 1 can add 10 to 20 nucleotides per second.
  • It only acts on the lagging strand.
  • DNA polymerase 1 adds nucleotides to the growing polynucleotide chain.
  • It removes the RNA primer from 5’ to 3’ direction.

Also Read: Difference Between Replication And Transcription

DNA Polymerase III

DNA polymerase III holoenzyme is the primary enzyme complex involved in prokaryotic DNA replication. It was discovered by Thomas Kornberg (son of Arthur Kornberg) and Malcolm Gefter in 1970. DNA polymerase III holoenzyme (Pol III HE) is an enzyme that catalyzes elongation of DNA chains during bacterial chromosomal DNA replication. Bacterial cells contain several distinct DNA polymerases.

Being the primary holoenzyme involved in replication activity, the DNA Pol III holoenzyme also has proofreading capabilities that corrects replication mistakes by means of exonuclease activity reading 3’→5′ and synthesizing 5’→3′. DNA Pol III is a component of the replisome, which is located at the replication fork.

In Escherichia coli, five DNA polymerases have been found and designated as DNA polymerase (I, II, III, IV, V), in order of their discovery. The main function of the third polymerase, Pol III, is duplication of the chromosomal DNA, while other DNA polymerases are involved mostly in DNA repair and translesion DNA synthesis. Together with a DNA helicase and a primase, Pol III HE participates in the replicative apparatus that acts at the replication fork.

Unlike other bacterial DNA polymerases, Pol III HE is a multi-subunit complex, in which twin catalytic subassemblies, called the Pol III core, are embedded with several other auxiliary subunits. Cooperative and coordinated action of these subunits enables Pol III HE to function as the chromosomal replicase, concurrently synthesizing the leading and lagging strands of DNA. DNA synthesis by Pol III HE is also characterized by a rapid chain-elongation reaction, high processivity, and high fidelity, all of which are essential for chromosomal DNA replication.

What You Need To Know About DNA Polymerase III

  • DNA polymerase III holoenzyme (Pol III HE) is an enzyme that catalyzes elongation of DNA chains during bacterial chromosomal DNA replication.
  •  It was discovered by Thomas Kornberg and Malcolm Gefter in 1970.
  • DNA polymerase 3 is encoded by dnaE, dnaQ and hole genes.
  • It belongs to the DNA polymerase family C.
  • DNA polymerase 3 requires an RNA primer to synthesize the DNA
  • It only has 3’ to 5’ exonuclease activity.
  • DNA polymerase 3 can add around 100 nucleotides per second.
  • It acts on both leading and lagging strands of the replication fork.
  • DNA polymerase 3 is the key enzyme for synthesizing DNA in prokaryotes.
  • It adds deoxyribonucleic acid to the 3’ end.

Also Read: Difference Between Template And Coding Strand

Difference Between DNA Polymerase I And III In Tabular Form

BASIS OF COMPARISON DNA Polymerase I DNA Polymerase III
Description DNA polymerase I also referred to as Pol I, manly functions to synthesize short stretches of DNA during excision repair and to remove RNA primers and fill the gaps between Okazaki fragments in lagging strand replication.   DNA polymerase III holoenzyme (Pol III HE) is an enzyme that catalyzes elongation of DNA chains during bacterial chromosomal DNA replication.  
Discovery It was discovered by Arthur Kornberg in 1956.   It was discovered by Thomas Kornberg and Malcolm Gefter in 1970.  
Encoding It is encoded by polyA gene.   It is encoded by dnaE, dnaQ and hole genes.  
Family It belongs to the DNA polymerase family A.   It belongs to the DNA polymerase family C.  
RNA Primer It removes the RNA primer.   It requires an RNA primer to synthesize the DNA.  
Exonuclease Activity It has both 3’ to 5’ exonuclease activity and 5’ to 3’ exonuclease activity.   It only has 3’ to 5’ exonuclease activity.  
Nucleotides Addition It can add 10 to 20 nucleotides per second.   It can add around 100 nucleotides per second.  
Action It only acts on the lagging strand.   It acts on both leading and lagging strands of the replication fork.  
Role It adds nucleotides to the growing polynucleotide chain.   It is the key enzyme for synthesizing DNA in prokaryotes.  
Function It removes the RNA primer from 5’ to 3’ direction.   It adds deoxyribonucleic acid to the 3’ end.  

Also Read: Difference Between Leading And Lagging Strand In DNA Replication