Types of DNA Polymerase

Proofread (check back for mistakes and remove them) exonuclease 3 5  

There s not just one DNA polymerase there s a whole army. DNA replication actually occurs in large complexes containing many proteins and sometimes many polymerases. In eukaryotic cells we have to replicate both mitochondrial and nuclear DNA, and there are specific DNA polymerases for each. In addition to DNA replication, you have to make new DNA when you repair. Consequently, the function may be specialized for repair or replication. There can also be specialization for making the leading or lagging strand. Some of the activities of DNA polymerases from eukaryotes and prokaryotes are shown in the table on the next page. 

DNA polymerases all synthesize new DNA using a template and make the new DNA in a 5 3 direction (new nucleotides are added to the 3 end). In addition to making DNA, some of the DNA polymerases can also hydrolyze it. An exonuclease works only on the ends of the DNA (or RNA), and like everything else about DNA, exonuclease activity has a direction too. The 3 5 exonuclease activity removes nucleotides from the 3 end (by hydrolyzing the phosophodi-ester bond). Since the chain grows in the 5 3 direction, polymerases that have a 3 5 exonuclease activity can look back over their work 

8 Eukaryotes Yes No Nuclear replication Continuous (leading) strand replication 

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Since rolling circle amplification takes place at a constant temperature, there is no need for the target amplification process to take place in a thermal cycler, which is required to regulate the temperature for different parts of the reaction. The type of DNA polymerase to be used in RCA is not limited to thermostable enzymes, like the PCR-based diagnostics. On the other hand, the RCA method requires the environment to be free of contaminations as the RCA arrays are highly sensitive. Wiltshire [22]... 

Information Metabolism Directions and Conventions DNA Replication Types of DNA Polymerase Recombination... 

Like bacteria, eukaryotes have several types of DNA polymerases. Some have been linked to particular functions, such as the replication of mitochondrial DNA. The replication of nuclear chromosomes involves DNA polymerase a, in association with DNA polymerase S. DNA polymerase a is typically a multisubunit enzyme with similar structure and properties in all eukaryotic cells. One subunit has a primase activity, and the largest subunit (Afr -180,000) contains the polymerization activity. However, this polymerase has no proofreading 3 —>5 exonuclease activity, making it unsuitable for high-fidelity DNA replication. DNA polymerase a is believed to function only in the synthesis of short primers (containing either RNA or DNA) for Okazaki fragments on the lagging strand. These primers... 

There are many different types of DNA polymerases, and they vary greatly in their activities and in the nature of the reactions they catalyze. Some polymerases are involved mainly in the replication of DNA. Others are used for the repair of damaged DNA. There is also an important difference between the enzymes isolated from eukaryotes and those isolated from prokaryotes. Most of the eukaryotic DNA polymerases that have been isolated so far have just the simple 5 —> 3 polymerization activity shown in equation 14.1. Prokaryotic DNA polymerases, however, are multifunctional. In addition to their 5 — 3 polymerase activity, they possess a 3 5 exonuclease activity that can excise incorporated... 

Distant relatives. The structure of adenylate cyclase is similar to the structures of some types of DNA polymerases, suggesting that these enzymes derived from a common ancestor. Compare the reactions catalyzed by these two enzymes. In what ways are they similar ... 

In eubacteria and eukaryotes, several types of DNA polymerases have been characterized three in eubacteria (DNA polymerases I, II and III), and five in eukaryotes (DNA polymerases a, 3, 6, e and )). Some of these enzymes, named DNA replicases , are specifically involved in DNA-chain elongation at the replication fork. They have a multi-subunit structure and can prime and perform DNA replication in a processive way when they are associated with the other replicative proteins. In eubacteria, only one DNA replicase has been isolated (DNA polymerase III), whereas several DNA replicases co-exist in eukaryotes DNA polymerases a, 6 and e, which are essential for the replication of nuclear DNA, and DNA polymerase y, which is responsible for the replication of the mitochondrial genome. The other eubacterial and eukaryotic DNA polymerases are monomeric and are preferentially involved in mechanisms which require replication of short DNA fragments, in the course of either DNA repair (DNA polymerases I and II from E. coli, eukaryotic DNA polymerase 3), or DNA replication (maturation of Okasaki fragments by E. coli DNA polymerase I). 

There are many types of DNA polymerases which can excise, fill gaps, proofread, repair and replicate. 

DNA polymerase. All organisms contain DNA polymerases that have different properties. Even some bacteriophages code for their own DNA polymerases. The type of DNA polymerase used in the dideoxy technirjue was chosen because it works the best. 

Subsequent reports described a syndrome of type B lactic acidosis in patients treated with zidovudine and other nucleoside reverse transcriptase inhibitors, including stavudine, lamivudine, and didanosine which has also been attributed to mitochondrial DNA toxicity [95-106]. There are five types of DNA polymerase in human cells that catalyze the synthesis of new complementary DNA from the original DNA template (HIV encodes a reverse transcriptase DNA polymerase which uses RNA as the template). The active triphosphate metabolites of zidovudine, didanosine, and stavudine inhibit DNA polymerase gamma in mitochondria, block the elongation of mitochondrial DNA, and deplete mitochondrial DNA [91-93,101,105-108]. The link between NRTl effects on mitochondrial DNA and lactic acidosis is not entirely clear but is most likely related to disturbances of oxidative phosphorylation and impaired pyruvate metabolism leading to lactate accumulation. 

Partially thiolated polycytidylic acid (MPC) and various thiolated DNA and RNA isolates inhibited the DNA polymerases of tumor viruses and showed some significant selectivities129,130) (see the article by Dr. Chandra in this volume for more information). Studies of the effects of two, partially thiolated polyribonucleotides on the various types of DNA polymerase activities... 

DNA polymerases. Several types of DNA polymerase make DNA by adding the deoxyribonucleotides dATP, dGTP, dTTP and dCTP to... 

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