Difference Between DNA Polymerase 1 2 and 3

Key Difference – DNA Polymerase 1 vs 2 vs 3
 

DNA polymerase is a special clade of enzymes which are involved in DNA replication of living organisms. Genetic information is passed from one generation to the next generation due to the presence of this enzyme. There are different forms of DNA polymerase enzyme found in eukaryotes and prokaryotes. DNA polymerase 1, 2 and 3 are found only in prokaryotic organisms, and they play different roles in DNA replication. The key difference between DNA polymerase 1 2 and 3 mainly relies on the prime function of each enzyme. DNA polymerase 3 is the main enzyme which catalyzes the DNA synthesis, while DNA polymerase 1 and 2 are involved in DNA repairing and proofreading.

CONTENTS
1. Overview and Key Difference
2. What is DNA Polymerase
3. What is DNA Polymerase 1
4. What is DNA Polymerase 2
5. What is DNA Polymerase 3
6. Side by Side Comparison – DNA Polymerase 1 vs 2 vs 3
7. Summary

What is DNA Polymerase?

DNA duplication is a must for passing genetic information from parent to offspring. This is facilitated by a special enzyme called DNA polymerase. DNA polymerase can be defined as a ubiquitous enzyme which catalyzes the synthesis of DNA complementary to the existing DNA in living cells. It was first discovered in E coli by Arthur Kornberg in 1955. DNA replication and maintenance are mainly governed by DNA polymerases in the cell. Discovery of DNA polymerases helped many techniques of molecular biology. It is the enzyme required to synthesis new DNA strands similar to the original DNA of the organisms from nucleotides during many molecular biological techniques including PCR, gene cloning, gene sequencing, disease diagnosis, gene therapy, polymorphism analysis, etc.

DNA polymerases exist in multiple forms differing from shape and size. They belong to several families: A, B, C, D, X, Y and RT. Prokaryotic DNA polymerases are grouped into five different categories namely, DNA polymerase 1, DNA polymerase 2, DNA polymerase 3, DNA polymerase 4 and DNA polymerase 5. Eukaryotic organisms have approximately fifteen different DNA polymerases namely polymerase β, λ, σ, μ, α, δ, ε, η, ι, κ, Rev1, ζ, γ, θ and ν.

When synthesizing new DNA by DNA polymerase, it starts from the 3’ end and directs the synthesis towards the 5’ end by adding nucleotides at a time, complementary to the template DNA. DNA polymerase needs a preexisting 3’ OH group to initiate the chain synthesis and is facilitated by the small DNA or RNA fragment called primer. DNA polymerase reads the template DNA and moves from 3’ end to 5’ end, making a new 5’-3’ DNA strand.

What is DNA Polymerase 1?

DNA polymerase 1 (Pol 1) is an enzyme found in prokaryotes which help in bacterial DNA replication. It is the first type of DNA polymerase discovered by Arthur Kornberg in 1956. This enzyme is present in all prokaryotic organisms. Pol 1 is encoded by the gene polA and is composed of 928 amino acids. It has a 5’ to 3’ exonuclease activity; thus, it is popular as a DNA repairing enzyme rather than a DNA replicating enzyme. It also has the ability to catalyze multiple polymerizations prior to releasing the template DNA, and connecting Okazaki fragments together by filling new DNA, and removing RNA primers.

Pol 1 isolated from E Coli was extensively used in molecular applications. However, once Taq Polymerase was discovered, it replaced the E Coli Pol 1 in PCR technology. Taq polymerase is kind of a thermostable DNA polymerase belonging to Pol 1.

What is DNA Polymerase 2?

DNA polymerase 2 (Pol 2) is a prokaryotic enzyme which catalyzes the DNA replication. It belongs to the polymerase B family and is encoded by the gen polB. It was first discovered from E Coli by Thomas Kornberg in 1970. Pol 2 is a globular protein composed of 783 amino acids. It has both 3’ to 5’ exonuclease activity and 5’ to 3’ polymerase activity. It interacts with DNA polymerase 3 enzymes to maintain the fidelity and processivity of DNA replication. Pol 2 also has the ability to proofread the newly synthesized DNA for accuracy.

What is DNA Polymerase 3?

DNA polymerase 3 (Pol 3) is the main enzyme which catalyzes the DNA replication in prokaryotes. It belongs to the family C polymerase and is encoded by the gene polC. It was discovered by Thomas Kornberg in 1970. Pol 3 is a component of replication fork and can add 1000 nucleotides per second to the newly polymerizing DNA strand.

Pol 3 is a holoenzyme composed of ten distinct proteins and has three functional molecules namely α, ε and θ. Three functional molecules of Pol 3 are separately responsible for three actions of the enzyme. The α subunit manages the polymerization of DNA while the ε manages the exonuclease proofreading activity of the pol 3 enzyme. The θ subunit helps the ε subunit for proofreading.

What is the difference between DNA Polymerase 1 and 2 and 3?

Summary – DNA Polymerase 1 vs 2 vs 3

DNA polymerase is an important enzyme class found in all living organisms. The main function of DNA polymerase is DNA replication. It is capable of assembling nucleotides and synthesizing new complementary DNA for existing DNA. This enzyme exists in different forms varying from shape and size. DNA polymerase 1, 2 and 3 are prokaryotic DNA polymerases involved in DNA replication. Pol 1 catalyzes the repairing of DNA damages. Pol 2 catalyzes the fidelity and processivity of DNA replication. Pol 3 catalyzes the 5’ to 3’ DNA polymerization.

Reference:
1. Lehman, I. R. “Discovery of DNA Polymerase.” Journal of Biological Chemistry. N.p., 12 Sept. 2003. Web. 06 Mar. 2017
2.Gardner, Andrew F., and Zvi Kelman. “DNA polymerases in biotechnology.” Frontiers. Frontiers, 13 Nov. 2014. Web. 06 Mar. 2017
3. Garcia-Diaz, Miguel, and Katarzyna Bebenek. “Multiple functions of DNA polymerases.” Critical reviews in plant sciences. U.S. National Library of Medicine, Mar. 2007. Web. 06 Mar. 2017

Image Courtesy:
1. “DNA polymerase”Di Yikrazuul – Opera propria (CC BY-SA 3.0) via Commons Wikimedia
2. “PolymeraseDomains” By (unknown) “Molecule of the Month”, March 2000 – Protein Data Bank (Public Domain) via Commons Wikimedia
3. “Pol2 structure (Based on 35KM)” By Sbandeka – Own work (CC BY-SA 4.0) via Commons Wikimedia
4. “DNA polymerase III (with subunits)” By Alepopoli – Own work (CC BY-SA 3.0) via Commons Wikimedia