Adding 3A overhang to a PCR product
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Procedure
- Purify the PCR product. Before adding the overhangs it is very important to remove all the Proofreading DNA Polymerase (Pfu) by purifying the PCR product carefully (e.g. with a commercial PCR purification kit or phenol extraction and DNA precipitation); since the proofreading activity of DNA Polymerase will degrade the A overhangs, creating blunt ends again.
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Prepare Taq DNA polymerase reaction mix for a typical 20 - 50 μl reaction:
Final Concentration Vol (μl) Purified PCR product 0.15 to 1.5 pmol Varieundefined dATP (10 mM) 0.2 mM 1 PCR Buffer with Mg (10x) 1x (1.5 mM MgCl2) 5 Taq DNA Polymerase (5 U/μl) 1U 0.2 ddH2O to 50 μl
~undefined The A-addition reaction works best when a specific amount of the PCR product is used. The recommended amount is 10�100 ng PCR product for each 100 bp length of the PCR product. This corresponds to 0.15�1.5 pmol PCR product (see table below).
PCR product size Amount of PCR product to use 100 bp 10�100 ng 250 bp 25�250 ng 1000 bp 100�1000 ng
- Incubate 20 min at 72 °C.
- Proceed to TA cloning. For optimal ligation efficiency, it''s best to use fresh PCR products, since 3´A-overhangs will gradually be lost during storage.
Note
Based on protocols from Qiagen and Finnzymes.