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From Proteopedia

Overview

DNA polymerase 3 is the primary enzyme responsible for prokaryotic DNA replication. It was first discovered by Thomas Kornberg and Malcolm Gefter in 1970. This polymerase works in conjunction with four other polymerases. These include polymerase 1,2,4, and 5.

Function

As mentioned DNA Polymerase 3 is responsible for replicating DNA in prokaryotes. It's activity starts after separation of strands at the origin of replication. The two most important subunits of this polymerase are the α subunit that links the nucleotides together via a phosphodiester bond and the ε subunit that ensures the bases are accurate via proofreading mechanisms. It can synthesize base pairs at a rate of about 1000 nucleotides per second and can only move in the 5' to 3' direction. One thing unique about this enzyme is the sliding clamp which is a donut shaped protein that allows the polymerase to bind to the DNA strands and move along it.

Structural highlights

This enzyme contains many different regions that all have different properties. These are the of the polymerase. The purple regions are towards the outside because they are polar and therefore hydrophilic. The gray regions are hydrophobic regions. This next scene shows the of the polymerase. This consists of alpha helices which are pink and beta pleated sheets which are yellow. These secondary structures form via hydrogen bonding between the amino acid backbones. Finally, another region we will talk about are the regions of the polymerase. These regions are another example of the hydrophilic aspects of the proteins. All 3 of these and so many others that we did not talk about go to show the extreme complexity of this beautiful and indispensable enzyme. It's a shame we aren't prokaryotes! :(

References

http://www.rcsb.org/structure/4GX8 https://www.sciencedirect.com/topics/medicine-and-dentistry/dna-polymerase-iii-holoenzyme