FAQ: Which DNA polymerase can I use to blunt DNA?

Note: dNTPs must be added to blunting reactions
We primarily recommend DNA Polymerase I, Large (Klenow) Fragment (M0210) for blunting. Optimal blunting activity is at room temperature (25°C).
T4 DNA Polymerase (M0203) can also be used to blunt but should be used at 12°C to prevent against the formation of recessed ends due to its very strong 3'-5' exonuclease activity.
For blunting at thermophilic temperatures, we recommend Vent (M0254) or Deep Vent (M0258) DNA Polymerase. While Q5 High-Fidelity Polymerase may also be used for blunting at thermophilic temperatures, it has very strict buffering requirements for optimal activity and should only be used with Q5 Reaction Buffer.
Mung Bean Nuclease (M0250) is our only catalog enzyme that can remove 5' overhangs.
For inactivation, we recommend heating + EDTA; please click here for our inactivation guidelines.

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DNA polymerases are often used to blunt by filling in protruding 5' ends (5´ → 3´ polymerization activity) and/or chewing back (3´ → 5´ exonuclease activity) 3' overhangs. 
In the absence of dNTPs, 3'-5' exonuclease activity will overwhelm the 5'-3' polymerase activity to remove more nucleotides than desired. However, 5'-3' polymerization activity is preferred by the enzyme compared to  3'-5' exonuclease activity in the presence of dNTPs. The presence of dNTPs ensures that nucleotides are filled back in across from the template, resulting in blunt ends.
For more information, please see our other FAQs:
What does exonuclease activity mean for a DNA polymerase?
What ends will my PCR products have?