One of the easiest methods for cloning blunt-ended DNA fragments including PCR products is T-vector cloning, such as with pGEM®-T or pGEM®-T Easy Vector Systems. This method takes advantage of the “A” overhang added by a PCR enzyme like Taq DNA Polymerase. T vectors are linearized plasmids that have been treated to add 3′ T overhangs to match the A overhangs of the insert. The insert is directly ligated to the T-tailed plasmid vector with T4 DNA ligase. The insert can then be easily transferred from the T vector to other plasmids using the restriction sites present in the multiple cloning region of the T vector.
Proofreading polymerases like Pfu do not add “A” overhangs so PCR products generated with these polymerases are blunt-ended. In a previous blog, we discussed a simple method for adding an A-tail to any blunt-ended DNA fragment to enable T-vector cloning. Below, we think about the next step: Ligation.
Tailing blunt-ended DNA fragments with TaqDNA Polymerase allows efficient cloning of these fragments into T-Vectors such as the pGEM®-T Vectors. This method also eliminates some of the requirements of conventional blunt-end cloning — Fewer steps, who can argue with that?
Q: Can PCR products generated with GoTaq® DNA Polymerase be used to for T- vector cloning?
A: Yes. GoTaq® DNA Polymerase is a robust formulation of unmodified Taq Polymerase. GoTaq®DNA Polymerase lacks 3’ →5’ exonuclease activity (proof reading) and also displays non-template–dependent terminal transferase activity that adds a 3′ deoxyadenosine (dA) to product ends. As a result, PCR products amplified using GoTaq® DNA Polymerase will contain A-overhangs which makes it suitable for T-vector cloning.
We have successfully cloned PCR products generated using GoTaq® and GoTaq® Flexi DNA Polymerases into the pGEM®-T (Cat.# A3600), pGEM®-T Easy (Cat.# A1360) and pTARGET™ (Cat.# A1410) Vectors.
Q: Can GoTaq® Long PCR Master Mix be used for T-Vector Cloning?
A: Yes it can. GoTaq® Long PCR Master Mix utilizes recombinant Taq DNA polymerase as well as a small amount of a recombinant proofreading DNA polymerase. This 3´→5´ exonuclease activity (proof reading) enables amplification of long targets. Despite the presence of a small amount of 3´→5´ exonuclease activity, the GoTaq® Long PCR Master Mix generates PCR products that can be successfully ligated into the pGEM®-T Easy Vector System.
We have demonstrated that GoTaq® Long PCR Master Mix successfully generated DNA fragments that could be ligated into pGEM®-T Easy Vector System without an A-tailing procedure, and with ligation efficiencies similar to those observed with the GoTaq® Green Master Mix.
You have PCR amplified your insert of interest, made sure the PCR product is A tailed and are ready to clone into a T vector (e.g., pGEM®-T Easy Vector). The next step is as simple as mixing a few microliters of your purified product with the cloning vector in the presence of DNA ligase, buffer and ATP, right? In fact, you may need to consider the molar ratio of T vector to insert.