DNA Polymerases

Enzymes that add dNTPs to recessed 3’ DNA ends (5’ extensions)

The Core Reaction: 5’→3’ Extension

One event, drawn three ways, they all mean this

Many Products, Three Activities

Distinguishing Features

New England Biolabs table comparing DNA polymerases by 5-prime to 3-prime exonuclease, 3-prime to 5-prime exonuclease, strand displacement, thermostability and other properties — Adapted from the NEB properties-of-DNA-polymerases table

5’→3’ Exonuclease Activity

This behavior is pretty rare
Taq and E. coli pol 1 have it

Strand Displacement

The more common scenario

Rolling Circle Replication

Phi29 is the pro at this

Application: Forensic Analysis with RCA

Kunkel Mutagenesis

Use T4 DNA Polymerase
(no 5’→3’ exo or displacement)

3’→5’ Exonuclease Activity

“Proofreading activity”
Major component determining fidelity
Absent in Taq-like enzymes
Present in Pfu-like enzymes
Without it, extension products typically contain a single 3’ “A” overhang