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Protocols / Exponential Megaprimer PCR (EMP)

The exponential megaprimer PCR (EMP) was used to replace the metal-binding-related sequences of our pORE-E3_2x35S_T4MBP by GFP. In theory, the EMP is based on two PCR reaction: while the insert is amplified by a standard PCR in the first (EMP1), the second places the insert in the final vector backbone already (EMP2). To try different weight ratios of vector backbone and megaprimer turned out be helpful in prior experiments. Since a correct nucleotide sequence was important here, the F-530 Phusion® High-Fidelity DNA Polymerase (Thermo Scientific) was used.

Workflow

1. Amplify the Megaprimer by standard PCR and dilute the purified product 1:10 before using it for the final EMP reaction.
2. Test different weight ratios of Vector:Megaprimer for the best EMP (Table 1).
   • Test different ratios of insert and vector DNA amounts. We recommend fours mixes: two with 10 and 20 ng of insert respectively as well as two mixes lacking the F1 oligonucleotide but containing 80 and 160 ng of insert respectively.
3. Modify the EMP2 product.
   • Phosphorylate its 5´ends (Table 2)
   • Circularize the EMP2 product by adding 1 µl ATP and 1 µl T4 DNA Ligase. Incubate the mix at 16 °C overnight and inactivate the enzyme for 10 min at 80 °C.
   • Degrade the source vector by adding 1 µl of DpnI. Incubate the mix for 15 min at 37 °C and inactivate the enzyme for 15 min at 80 °C.
4. Transfer the EMP product into competent bacteria.

Table 1: EMP Mixes and Temperature Program

Table 2: Phosphorylation Mix and Temperature Program