15. Prokaryotic DNA polymerases
DNA pol I also known as Kornberg enzyme. First DNA polymerase discovered in E. coli.
Discovered by Arthur Kornberg (won Nobel price for this discovery). Single polypeptide of 928
amino acid residues. Performs functions including primal removal (with 5ˊ 3ˊ exonuclease
activity), gap filling (5ˊ 3ˊ polymerase activity) and DNA repair.
16. Prokaryotic DNA polymerases
DNA pol II is monomeric protein and has 5ˊ 3ˊ polymerase and 3ˊ 5ˊ exonuclease activity. Low
processivity and low polymerization rate. Alternative DNA polymerase involved in DNA repair and
can replicate DNA if the template is damaged.
DNA pol III primary enzymes involved in DNA replication. It is multimeric protein complex
consisting of 10 different polypeptides. Hallmark is High polymerization rate and high
processivity. It has 5ˊ 3ˊ polymerase and 3ˊ 5ˊ exonuclease activity.
DNA polymerase IV (Din B) and DNA polymerase V (umuD2C) are Y-family DNA polymerases.
Members of Y-family do not contain 3ˊ 5ˊ exonuclease activity. Characterized by low catalytic
efficiency, low processivity and low fidelity. Involved in translesion synthesis and replicate
damaged DNA by bypassing damaged nucleotides that would otherwise block normal
progression of replication fork.
DNA pol III primary enzymes involved in DNA replication. It is multimeric protein complex
consisting of 10 different polypeptides. Hallmark is High polymerization rate and high
processivity. It has 5ˊ 3ˊ polymerase and 3ˊ 5ˊ exonuclease activity.
DNA polymerase IV (Din B) and DNA polymerase V (umuD2C) are Y-family DNA polymerases.
Members of Y-family do not contain 3ˊ 5ˊ exonuclease activity. Characterized by low catalytic
efficiency, low processivity and low fidelity. Involved in translesion synthesis and replicate
damaged DNA by bypassing damaged nucleotides that would otherwise block normal
progression of replication fork.
17. Enzyme DNA pol I DNA pol II DNA pol III
Structural gene PolA polB dnaE, dnaQ,
holE, dnaN,
dnaX, holC, holD
etc
Subunits (different types) 1 1 10
3’ 5’ exonuclease yes yes Yes
5’ 3’ exonuclease Yes No No
Polymerization rate
(nucleotides/sec)
~10-20 ~40 ~1000
Processivity (nucleotides
added before polymerase
dissociates)
~200 ~1500 ~50000
Function DNA repair, Gap
filling and primer
removal
DNA repair Main replicating
enzyme
Prokaryotic DNA polymerases
29. Replication fork
The replication fork is a Y-shaped region where a DNA double helix has been
unwound and separated to create an area where DNA polymerases and the other
enzymes involved can use each strand as a template to synthesize a new double helix
It is called a fork because the structure resembles a two-pronged fork.
32. Leading and Lagging strands
Leading strand- A new strand that is synthesized continuously during
replication
Lagging strand- A new strand that is synthesized in short fragment which are
later joined together
Okazaki fragments- Short fragments of DNA that are result of lagging strand
synthesis
33. Others
Ligase- The enzyme that joins together the DNA fragments by catalyzing the
formation of bond between 3’-OH group and 5’-phosphate group on sugar
phosphate backbone
DNA polymerase I and DNA polymerase III
