Introduction of DNA Polymerase Family
DNA polymerases are a group of enzymes that are integral to the processes of DNA replication, repair and recombination. It mainly includes palm domain, finger domain and thumb domain, among which the finger domain is in charge of the binding of dNTP, the palm domain controls the incorporation of catalytic dNTP, and the thumb domain is related to the continuous synthesis ability of DNA. The DNA polymerase family is responsible for adding nucleotides to the 3'-OH end of the growing DNA strand to synthesize a new DNA strand. These versatile enzymes can be found in a wide range of organisms ranging from bacteria, viruses, and eukaryotes.
Classification of DNA Polymerase Family
Currently, DNA polymerases can be divided into seven different subfamilies based on sequence similarity: A, B, C, D, E, F and RT. The most important factor determining the different functions of DNA polymerases is the structure of the thumb and finger domains, as in the case of Taq DNA polymerase, T7 DNA polymerase and Bst polymerase, which belong to the A family of DNA polymerases, there are still significant differences in heat resistance and strand replacement capacity. There are also significant differences in the heat resistance and strand substitution capacity. In addition, some additional structural domains provide additional functions such as 3'-5' end exonuclease and 5'-3' end exonuclease activity.
| Family |
Types of DNA Polymerase |
Species |
DNA Polymerases |
| A |
Replicative and repair polymerases |
Eukaryotic and prokaryotic |
T7 DNA polymerase, Pol I, and DNA Polymerase γ |
| B |
Replicative and repair polymerases |
Eukaryotic and prokaryotic |
Pol II, Pol B, Pol ζ, Pol α, δ, and ε |
| C |
Replicative polymerases |
Prokaryotic |
Pol III |
| D |
Replicative polymerases |
Euryarchaeota |
Not well-characterized |
| X |
Replicative and repair polymerases |
Eukaryotic |
Pol β, Pol σ, Pol λ, Pol μ, and Terminal deoxynucleotidyl transferase |
| Y |
Replicative and repair polymerases |
Eukaryotic and prokaryotic |
Pol κ, Pol η, Pol IV, and Pol V |
| RT |
Replicative and repair polymerases |
Viruses, retroviruses, and Eukaryotic |
Telomerase, Hepatitis B virus |
Function of DNA Polymerase Family
3'-5' exonuclease activity: The polymerase is able to cleave just introduced nucleotides and correct errors (proofreading).
5'-3' exonuclease activity: The polymerase is able to cleave nucleotides in the direction of polymerization, thus enabling DNA repair. This activity is also used to remove attached probes when the complementary strand is synthesized.
Strand Displacement: Polymerases are capable of displacing downstream DNA encountered during synthesis. If the polymerase also has 5'-3' exonuclease activity, the displaced DNA will be destroyed. If not, leave it intact.
Tolerance: Polymerases can use uracil-containing templates as well as dUTP during polymerization. Addition of uracil is a common technique to prevent cross-contamination.
Key Factors in Choosing the Right DNA Polymerase
Thermostability: The ability of DNA polymerase to withstand high temperatures. The thermostability of different DNA polymerases varies greatly, which is generally reflected by the half-life.
Fidelity: The ability of a DNA polymerase to make precise copies of a DNA template. Some DNA polymerases have 3'-5' exonuclease activity, which can correct wrong bases, and the fidelity can be reflected by the mismatch rate.
Sensitivity: The ability of DNA polymerase to amplify low-copy templates can be reflected by the detection rate.
Specificity: The ability of DNA polymerase to amplify only the target fragment during the PCR process. DNA polymerase is often modified by antibody method or ligand method to improve enzyme specificity.
Amplification speed: The rate at which DNA polymerase incorporates nucleotides into new strands of DNA. High amplification rate DNA polymerases can speed up the overall experiment time.
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