PCR Using Hot Start Taq DNA Polymerase (M0495)
The following guidelines are provided to ensure successful PCR using New England Biolabs’ Hot Start Taq DNA Polymerase. These guidelines cover routine PCR. Amplification of templates with high GC content, high secondary structure, low template concentrations, or amplicons greater than 5 kb may require further optimization.
Due to the hot start nature of the enzyme, reactions can be assembled on the bench at room temperature and transferred to a thermocycler. No separate activation step is required to release the inhibitor from the enzyme.
Add to a sterile thin-walled PCR tube:
|Component||25 μl reaction||50μl reaction||Final Concentration|
|10X Standard Taq
|2.5 µl||5 μl||1X|
|10 mM dNTPs||0.5 µl||1 μl||200 µM|
|10 µM Forward Primer||0.5 µl||1 μl||0.2 μM (0.05–1 μM)|
|10 µM Reverse Primer||0.5 µl||1 μl||0.2 μM (0.05–1 μM)|
|Hot Start Taq
|0.125 µl||0.25 µl||1.25 units/50 µl
|Template DNA||variable||variable||< 1,000 ng|
|Nuclease-free water||to 25 µl||to 50 µl|
Transfer PCR tubes to a PCR machine and begin thermocycling:
Thermocycling conditions for a routine PCR:
Use of high quality, purified DNA templates greatly enhances the success of PCR. Recommended amounts of DNA template for a 50 μl reaction are as follows:
DNA Amount Genomic 1 ng–1 µg Plasmid or viral 1 pg–1 ng
Oligonucleotide primers are generally 20–40 nucleotides in length and ideally have a GC content of 40–60%. Computer programs such as PrimerSelect™ and Primer3 can be used to design or analyze primers. The final concentration of each primer in a PCR may be 0.05–1 μM, typically 0.1–0.5 μM.
- Mg++ and additives:
Mg++ concentration of 1.5–2.0 mM is optimal for most PCR products generated with Hot Start Taq DNA Polymerase. The final Mg++ concentration in 1X Standard Taq Reaction Buffer is 1.5 mM. This supports satisfactory amplification of most amplicons. However, Mg++ can be further optimized in 0.5 or 1.0 mM increments using MgCl2 (NEB# B9021).
Amplification of some difficult targets, like GCrich sequences, may be improved with additives, such as DMSO (1) or formamide (2).
The final concentration of dNTPs is typically 200 μM of each deoxynucleotide.
- Hot Start Taq DNA Polymerase Concentration:
We generally recommend using Hot Start Taq DNA Polymerase at a concentration of 25 units/ml (1.25 units/50 μl reaction). However, the optimal concentration of Hot Start TaqDNA Polymerase may range from 5–50 units/ml (0.25–2.5 units/50 μl reaction) in specialized applications.
No separate activation step is required to release the hot start inhibitor from the enzyme. An initial denaturation of 30 seconds at 95°C is sufficient for most amplicons from pure DNA templates. For difficult templates such as GCrich sequences, a longer denaturation of 2–4 minutes at 95°C is recommended prior to PCR cycling to fully denature the template. With colony PCR, an initial 5 minute incubation at 95°C is recommended to lyse cells.
During thermocycling a 15–30 second denaturation at 95°C is recommended.
The annealing step is typically 15–60 seconds. Annealing temperature is based on the Tm of the primer pair and is typically 45–68°C. Annealing temperatures can be optimized by doing a temperature gradient PCR starting 5°C below the calculated Tm. We recommend using NEB's Tm Calculator to determine appropriate annealing temperatures for PCR. When primers with annealing temperatures above 68°C are used, a 2-step PCR protocol is possible (see #10).
The recommended extension temperature is 68°C. Extension times are generally 1 minute per kb. A final extension of 5 minutes at 68°C is recommended.
- Cycle number:
Generally, 25–35 cycles yield sufficient product. Up to 45 cycles may be required to detect low-copy-number targets.
- 2-step PCR:
When primers with annealing temperatures above 68°C are used, a 2-step thermocycling protocol is possible.
Thermocycling Conditions for a Routine 2-Step PCR:
STEP TEMP TIME Initial Denaturation 95°C 30 seconds 30 Cycles 95°C 15–30 seconds 68°C 1 minute/kb Final Extension 68°C 5 minutes Hold 4-10°C
- PCR product:
The PCR products generated using Hot Start Taq DNA Polymerase contain dA overhangs at the 3´ end; therefore the PCR products can be ligated to dT/dU-overhang vectors.
1. Sun, Y., Hegamyer, G. and Colburn, N. (1993). Biotechniques. 15, 372-374.
2. Sarkar, G., Kapelner, S. and Sommer, S.S. (1990). Nucleic Acids Res.. 18, 7465.