KOD polymerase bound to a DNA primer–template duplex, shown in gold. This research construct is not a commercial hot-start formulation. Rendering by EnzymeNews using Mol*, based on PDB 4K8Z (Bergen et al., 2013); colours are illustrative.
A polymerase advertised for long DNA fragments may look like the obvious choice for a demanding PCR project. Yet a maximum length on a product page tells only part of the story. Long-range DNA polymerases are tested with particular templates, formulations and reaction conditions, making the headline numbers difficult to compare directly.
This guide revisits products from the six suppliers covered in our original 2023 article. The figures below come from manufacturer documentation reviewed for this update. They are reported capabilities, not results of an independent head-to-head test by Enzyme News.
Why the starting DNA matters
Copying a long region of human genomic DNA is different from amplifying a fragment from a plasmid or a phage. DNA quality, sequence composition and template complexity all affect the outcome. A length demonstrated with one starting material should therefore retain that qualification when it is quoted.
Fidelity describes a different property: copying accuracy. An enzyme can offer high fidelity without being the best choice for every long target. Conversely, successful amplification of a long fragment does not establish how often copying errors occur.
Six products, different strengths and applications
Takara PrimeSTAR GXL. Takara reports amplification of up to 30 kb from human genomic DNA, 40 kb from lambda DNA and 13.5 kb from human cDNA. The template labels are essential: quoting “up to 40 kb” alone would imply a broader claim than those demonstrations support. Manufacturer documentation.
KOD Hot Start, distributed by Merck/Sigma-Aldrich. Manufacturer documents quote different maximum lengths. The 2011 TB341 manual lists 12 kb for genomic DNA and 20 kb for phage or plasmid DNA; other manufacturer material lists 12 kb and 21 kb, respectively. Check the current instructions for the exact catalogue product and ask the supplier to resolve conflicting specifications before planning a demanding experiment. TB341 manual; manufacturer overview.
Thermo Fisher Platinum SuperFi II. Thermo Fisher describes amplification of targets up to 20 kb, including a demonstration with human genomic DNA. The product is intended for high-fidelity applications such as cloning. As with the other products, the stated length is a demonstrated capability under specified conditions rather than a guarantee for every sequence. Manufacturer information.
New England Biolabs Q5 Hot Start. NEB’s specifications list maximum product lengths of 20 kb for simple templates and 10 kb for complex templates for standard Q5 polymerases. Its examples of complex templates include human and other mammalian genomic DNA. The higher limits of 30 kb and 20 kb are assigned specifically to Q5-XT Hot Start Master Mix; they should not be transferred to the standard Q5 Hot Start formulation. Product page; specifications and Q5-XT footnote.
Roche KAPA HiFi. The library-amplification kits discussed in the original article are designed to copy populations of adapter-ligated fragments for next-generation sequencing. That application emphasises representation and amplification bias, and is different from producing one very long genomic amplicon. KAPA EvoAmp ReadyMix also uses KAPA HiFi technology, but remains a distinct product formulation. KAPA HiFi library amplification; KAPA EvoAmp.
Agilent PfuUltra II Fusion HS. Agilent reports amplification of genomic targets up to 19 kb. This is a template-specific manufacturer claim, with performance depending on the sequence and reaction setup. Manufacturer specifications.
Reading beyond the biggest number
A useful comparison starts with the application and exact catalogue product. Relevant questions include the type and condition of the template, required copying accuracy, compatibility with downstream analysis and the evidence behind the stated performance.
Manufacturers may use different fidelity assays and difficult-template examples, so promotional multipliers do not automatically form a common ranking. Prices also vary by region, pack size and formulation. This guide does not identify a universal winner or rank cost-effectiveness.
For a different part of the molecular-biology toolkit, read about R2D ligase and joining DNA to RNA. Polymerases extend a strand by copying a template; ligases join existing pieces.
Update note, 27 September 2026: This guide was revised to clarify template-specific manufacturer claims, distinguish standard Q5 from Q5-XT, and explain the conflicting KOD documentation. The original publication date and URL are retained.
Image sources
- Structure: PDB 4K8Z, KOD polymerase research construct in a primer–template DNA complex. Bergen, K., Betz, K., Welte, W., Diederichs, K. and Marx, A. (2013). Structures of KOD and 9N DNA Polymerases Complexed with Primer Template Duplex. ChemBioChem, 14, 1058–1062. DOI: 10.1002/cbic.201300175.
- Visualization: original EnzymeNews rendering with Mol*, using RCSB PDB coordinate data. This research construct contains D141A/E143A substitutions and does not represent a commercial hot-start formulation or a comparison of the six products.
