Klenow fragment is the largest segment of DNA polymerase Ⅰ. It lacks the 5’ to 3’ exonuclease domain of the DNA polymerase Ⅰ. Here, let’s look at some more differences between the Klenow Fragment and DNA Polymerase Ⅰ.
Table of Contents
- DNA Polymerase Ⅰ
- Klenow Fragment
- Difference between Klenow Fragment and DNA Polymerase Ⅰ
- Frequently Asked Questions
DNA Polymerase Ⅰ
The five DNA polymerases that are known in E.coli and other prokaryotes are – DNA polymerase Ⅰ, DNA Polymerase Ⅱ, DNA Polymerase Ⅲ, DNA Polymerase Ⅳ and DNA PolymeraseⅤ. Out of these, DNA Polymerase Ⅲ is meant for actual DNA replication whereas the one and two are mostly meant for DNA repair.
DNA polymerase Ⅰ was isolated by Arthur Kornberg and was suggested as the first enzyme to be involved in the process of DNA replication. But, the enzyme is now considered to be a DNA repair enzyme rather than a replication enzyme. DNA polymerase Ⅰ is known to have 5 active sites which are as follows:
- Primer site
- Template site
- Exonuclease site (5’ to 3’ cleavage site)
- Exonuclease site (3’ to 5’)
- Nucleoside triphosphate site
Also, all DNA polymerases have 3 distinct domains – the 5′ to 3′ polymerase, 5′ to 3′ exonuclease and 3′ to 5′ exonuclease or proofreading domains. They also comprise subdomains, namely – the thumb domain, palm domain and fingers domain.
DNA polymerase Ⅰ is mainly involved in the removal of RNA primers from the precursor or Okazaki fragments and fills the resultant gaps with its 5’ to 3’ polymerisation capacity. This enzyme can also remove thymine dimers that are created due to UV-irradiation and also fills the resultant gap due to excision. This is the unique editing or proofreading function of the DNA polymerase Ⅰ.
Klenow Fragment
When E. coli DNA polymerase 1 is proteolytically digested by the bacterial protease subtilisin, it produces two fragments – a large fragment and a small fragment. The Klenow fragment is the largest fragment that contains 5′ to 3′ polymerase and 3′ to 5′ exonuclease (proofreading) activity domains of the DNA polymerase Ⅰ. The Klenow fragment’s 3′ to 5′ exonuclease activity aids in the elimination of improperly inserted bases while polymerisation proceeds. It lacks the 5′ to 3′ exonuclease activity, which is shown by full-length or entire E. coli DNA polymerase Ⅰ. Also, it is useful only when the polymerisation activity is required. Klenow fragments are used to fill 5′ overhangs, sequence DNA, and synthesise dsDNA, probes and proteins.
The Klenow fragment’s 3′ to 5′ exonuclease activity can also be undesirable sometimes. It can be deleted by changing the gene that codes for the Klenow fragment. The exo-Klenow fragment is the final by-product of this process. As a result, the exo-Klenow fragment possesses solely the 5′ to 3′ polymerase activity of E. coli polymerase 1.
Also Check:MCQs on DNA Replication
Difference between Klenow Fragment and DNA Polymerase Ⅰ
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Klenow Fragment |
DNA Polymerase Ⅰ |
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It is the largest fragment of DNA Polymerase Ⅰ. |
It is a polymerase enzyme in E.coli that is involved in DNA repair. |
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It has only two domains. |
It has three domains. |
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It lacks a 5’ to 3’ exonuclease domain. |
It has a 5’ to 3’ exonuclease domain. |
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The Klenow fragment is useful only when the polymerisation activity is required. It is used to fill 5′ overhangs, sequence DNA, and synthesise dsDNA, probes and proteins. |
DNA polymerase Ⅰ is mainly involved in the removal of RNA primers from the precursor or Okazaki fragments and fills the resultant gaps with its 5’ to 3’ polymerisation capacity. It also proofreads polymerase errors. |
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Difference between RNA Polymerase Core and RNA Polymerase Holoenzyme |
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