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# K242020

Product FAQ

## I am searching for a cloning vector that has gateway compatible att sites present in the vector for later transfer to an expression vector. A directional cloning bias would be a huge advantage. Do you have any suggestions?

We would suggest using one of our pENTR D-TOPO™ kits for easy TOPO™ cloning of your insert with the advantage of directionality.

Product FAQ

## What is the best molar ratio of PCR product:vector to use for TOPO™ TA cloning? Is there an equation to calculate the quantity to use?

We suggest starting with a molar ratio of 1:1 (insert:vector), with a range of 0.5:1 to 2:1. The quantity used in a TOPO™ cloning reaction is typically 5-10 ng of a 2 kb PCR product.

Equation:

length of insert (bp)/length of vector (bp) x ng of vector = ng of insert needed for 1:1 (insert:vector ratio)

Product FAQ

## Can I use a Taq polymerase to generate my gene of interest for directional TOPO™ cloning?

No, your gene of interest must be amplified with a proofreading polymerase such as AccuPrime™ Pfx or Platinum™ Pfx that leaves blunt ends for directional TOPO™ cloning.

Product FAQ

## I am using a Directional TOPO™ Cloning vector for cloning my PCR product. I have screened a bunch of colonies but they all contain my insert cloned in the reverse direction. How can I solve this problem?

Here are possible causes and suggestions:

- Incorrect PCR primer design: Make sure that the forward PCR primer contains the sequence, CACC, at the 5' end. The 4 nucleotides, CACC, base pair with the overhang sequence, GTGG, in the Directional TOPO™ vector.
- Reverse PCR primer is complementary to the GTGG overhang at the 5' end: Make sure that the reverse PCR primer does not contain the sequence, CACC, at the 5' end.
- Use a thermostable, proofreading polymerase such as Accuprime™ Pfx DNA Polymerase (Cat. No. 12344024) to produce blunt-end PCR products.

Product FAQ

## Your Gateway™-adapted TOPO™ vectors are supplied with a control template and control primers. Can I obtain the sequence of the control template?

The sequence of the control template is proprietary.

Product FAQ

## What is the best ratio of insert:vector to use for cloning? Is there an equation to calculate this?

You may have to try different ratios ranging from 1:1 to 15:1 insert:vector.

Equation:

length of insert (bp)/length of vector (bp) x ng of vector = ng of insert needed for 1:1 insert:vector ratio

Product FAQ

## Which PCR polymerases do you recommend for TA/Blunt/D-TOPO cloning and why?

TA Cloning:
- This cloning method was designed for use with pure Taq polymerases (native, recombinant, hot start); however, High Fidelity or Taq blends generally work well with TA cloning. A 10:1 or 15:1 ratio of Taq to proofreader polymerase will still generate enough 3' A overhangs for TA cloning.
- Recommended polymerases include Platinum™ Taq, Accuprime™ Taq, Platinum™ or Accuprime™ Taq High Fidelity, AmpliTaq™, AmpliTaq Gold™, or AmpliTaq Gold™ 360.

Blunt cloning:
- Use a proofreading enzyme such as Platinum™ SuperFi™ DNA Polymerase.

Directional TOPO cloning:
- Platinum™ SuperFi™ DNA Polymerase works well.

Product FAQ

## I’m getting low cloning efficiency with my directional TOPO™ cloning reaction. What should I do?

Here are suggestions to try to increase your cloning efficiency with dTOPO™ cloning:

- Ensure that the 5’ primer has CACC and the 3’ primer does not have sequence similarity to GTGG.
- The molar ratio of PCR product: TOPO™ vector used is critical to success.

We recommend using a 1:1 to 2:1 molar ratio, starting with a 1:1 of PCR product: TOPO™ vector. The TOPO™ cloning efficiency decreases significantly if the ratio of PCR product: TOPO™ vector is <0.1:1 or >5:1. These results are generally obtained if too little PCR product is used (i.e., PCR product is too dilute) or if too much PCR product is used in the TOPO™ cloning reaction. If the yield of the PCR product has been quantitated, the concentration of the PCR product may need to be adjusted before proceeding to TOPO™ cloning. For pENTR™ TOPO™ vectors, using 1-5 ng of a 1 kb PCR product or 5-10 ng of a 2 kb PCR product in a TOPO™ cloning reaction generally results in a suitable number of colonies.

Product FAQ

## I am cloning my gene of interest into the pENTR/SD/D-TOPO vector, but plan on expressing my gene in both E.coli and mammalian cells. Will the Shine-Dalgarno sequence interfere with mammalian expression?

No, the Shine-Dalgarno sequence does not adversely affect mammalian expression when used in an appropriate mammalian DEST vector.

Product FAQ

## What PCR enzyme would you recommend for use with the Directional TOPO™ Cloning Kits?

For the Directional TOPO™ Cloning Vectors, a PCR product must be generated by a proofreading enzyme to create a blunt product. Pfx50™ or Accuprime™ Pfx and Accuprime™ Pfx Supermix from Thermo Fisher Scientific are recommended for use.

When cloning a Pfx-amplified PCR product, the insert to vector ratio is an important consideration. The PCR product generally needs to be diluted since Pfx generates a high concentration of product and using too much insert DNA can hamper the TOPO™ reaction. A 1:1 molar ratio of vector to insert (or about 2-10ng of insert) is recommended.

Product FAQ

## What does “SD” stand for in pENTR/SD/D-TOPO™ vectors?

SD stands for Shine Dalgarno, which is a bacterial ribosomal binding site for efficient initiation of expression in E.coli.

Product FAQ