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DNA Polymerases: Types, Roles and Significance in BiotechnologyBY: ILA RUCHIE | Category: DNA | Submitted: 2016-01-19 06:57:26
Article Summary: "DNA molecules are the troves of genetic information of an organism. DNA is the basis of life and is transferred from parent to offspring's. The DNA content of the parent is doubled by means of replication mechanism aided by a specific enzyme, DNA polymerases. DNA polymerase plays a central role in process of life and carries a w.."
INTRODUCTION TO DNA POLYMERASES
DNA molecules are the troves of genetic information of an organism. DNA is the basis of life and is transferred from parent to offspring’s. The DNA content of the parent is doubled by means of replication mechanism aided by a specific enzyme, DNA polymerases. DNA polymerase plays a central role in process of life and carries a weighty responsibility of making an accurate copy of the cell’s genome. The DNA polymerases are enzymes that create DNA molecules by assembling nucleotides, the building blocks of DNA. The first evidence of the existence of an enzymatic activity capable of synthesizing DNA came in 1958 with the discovery of E. coli Pol I by A. Kornberg and colleagues. DNA polymerase moves along the old strand in the 3'-5' direction, creating a new strand having a 5'-3' direction.
CLASSIFICATION OF DNA POLYMERASES
Based on sequence homology and the comparison of the features of their primary sequence DNA polymerases are classified into seven families. A, B, C, D, X, Y, and RT.
TYPES AND ROLES OF DNA POLYMERASES (REPLICATIVE AND REPAIRATIVE)
1. Prokaryotic DNA polymerase
Prokaryotes contain five different types of DNA polymerase. These are described below.
2. Eukaryotic DNA polymerase
DNA polymerase ?
DNA polymerase ?
DNA polymerase β
Polymerases λ, σ and μ (lambda, sigma, and mu)
Polymerases η, ι and κ (eta, iota, and kappa)
Polymerases ζ (zeta)
Polymerases γ and θ (gamma and theta)
Retrovirus reverse transcriptase
SIGNIFICANCE OF DNA POLYMERASES IN BIOTECHNOLOGY
DNA polymerases also play central roles in modern molecular biology and biotechnology, enabling techniques including DNA cloning, the polymerase chain reaction (PCR), DNA sequencing, single nucleotide polymorphism (SNP) detection, whole genome amplification (WGA), synthetic biology, and molecular diagnostics.
THERMOSTABLE DNA POLYMERASE
Taq DNA polymerase. The original report of this enzyme, purified from the hot springs bacterium Thermus aquaticus, was published in 1976. Later, the polymerase chain reaction was developed and shortly thereafter "Taq" became a household word in molecular biology circles.
The thermophilic DNA polymerases, like other DNA polymerases, catalyze template-directed synthesis of DNA from nucleotide triphosphates. A primer having a free 3' hydroxyl is required to initiate synthesis and magnesium ion is necessary. In general, they have maximal catalytic activity at 75 to 80C, and substantially reduced activites at lower temperatures. At 37C, Taq polymerase has only about 10% of its maximal activity.
In addition to Taq DNA polymerase, several other thermostable DNA polymerases have been isolated and expressed from cloned genes. Three of the most-used polymerases are described in the following table:
Engineered DNA polymerases will continue to play important roles in biotechnology and the delivery of health care. Over the next several years, molecular methods that are easier, cheaper, and faster will emerge. At the same time, molecular biology will move toward analysis of low concentration biomolecules (i.e., a single set of chromosomes). Novel amplification techniques are also required to profile genetic variations among single cells because the quantity of genomic DNA from a single cell is insufficient to sequence directly. Therefore, DNA must first be amplified prior to further analysis. Furthermore, DNA polymerases with very low error rates are needed to ensure that long, amplified DNA are exact copies of the starting material.
Therefore, novel DNA amplification systems are needed to accelerate progress in emerging technologies and to make high-fidelity in vitro genome analysis and manipulation routine. Engineered DNA polymerases or cellular replication machineries capable of amplifying large DNA fragments have the potential to enable single cell genomics, genome synthesis, and manipulation. This issue summarizes the known properties of various DNA polymerase systems and how DNA polymerases are currently being manipulated to meet these growing demands.
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