Gibson Assembly
Gibson Assembly is a one-step, scarless method for joining multiple DNA fragments that share homologous end sequences. All fragments are combined with three enzymes in a single tube at 50 °C: a 5′ exonuclease chews back one strand to expose complementary single-stranded overhangs, a DNA polymerase fills the resulting gaps, and a DNA ligase seals the nicks. Because the join is directed by sequence homology rather than restriction sites, the assembly leaves no scar and does not depend on the vector containing convenient enzyme sites.
How does Gibson Assembly work?
The three enzymes act in sequence in a single isothermal reaction, usually 15 minutes for two fragments or 60 minutes for four or more.
- T5 exonuclease digests 5′ ends, exposing single-stranded 3′ overhangs on each fragment.
- Complementary overhangs from adjacent fragments anneal, setting the assembly order.
- Phusion DNA polymerase fills the remaining gaps.
- Taq DNA ligase seals the nicks, producing a covalently closed molecule.
- T5 exonuclease is heat-labile and is inactivated during the incubation, so it does not chew back the assembled product.
How long should the overlap be?
The original Gibson protocol used 40 bp overlaps. In practice 15–25 bp is sufficient for most two- to four-fragment assemblies, and NEB's HiFi protocol specifies a minimum of 16 bp. Longer overlaps improve efficiency for larger assemblies but make primers more expensive and more prone to secondary structure. Aim for an overlap melting temperature at or above 48 °C, and avoid overlaps with strong hairpins or repeated sequence.
How do I design the primers?
Each primer has two parts: a 3′ annealing region that binds the template, and a 5′ tail that carries the homology to the neighbouring fragment. The annealing region is what determines your PCR conditions; the tail is not part of the template and must be excluded from the annealing temperature calculation.
- Annealing region: 18–25 nt, Tm around 60 °C, calculated on the binding portion only.
- 5′ tail: 15–25 nt matching the end of the adjacent fragment exactly.
- Set the PCR annealing temperature from the annealing region for the first few cycles; the full-length primer Tm rises once the tail is incorporated.
- Check the assembled junction for frame shifts if you are fusing coding sequences.
When should I use something else?
Gibson is the wrong tool when you need to assemble many variants combinatorially from a fixed part library — Golden Gate's defined 4 nt overhangs are better suited, and the reaction can be run as a one-pot digest-ligate cycle. Gibson also struggles with fragments that share repeated sequence, because homologous regions elsewhere in the construct can anneal in the wrong place. For a single insert into a vector that already has convenient unique sites, classical restriction cloning is cheaper and needs no custom primers.
Typical Gibson Assembly reaction parameters
| Parameter | Typical value | Notes |
|---|---|---|
| Overlap length | 15–25 bp | NEBuilder HiFi specifies a 16 bp minimum; the original protocol used 40 bp |
| Overlap Tm | ≥ 48 °C | Below this, annealing becomes the limiting step |
| Incubation | 50 °C | Isothermal — no cycling |
| Time, 2–3 fragments | 15 min | Longer incubation gives little benefit |
| Time, 4–6 fragments | 60 min | Efficiency drops as fragment count rises |
| Vector amount | 50–100 ng | Keep total DNA under roughly 0.2 pmol |
| Insert : vector ratio | 2:1 to 3:1 molar | Use 1:1 for fragments over 10 kb |
Frequently asked questions
- How long does Gibson Assembly take?
- The assembly reaction itself is 15 minutes at 50 °C for two or three fragments, or 60 minutes for four or more. Including PCR amplification of the fragments, gel purification and transformation, a full Gibson cloning workflow typically takes one working day before colonies are ready to screen the following morning.
- How many fragments can Gibson Assembly join at once?
- Gibson Assembly routinely joins two to six fragments in one reaction. Efficiency falls as fragment count rises, so assemblies of more than six pieces are usually staged in rounds. The original 2009 publication demonstrated assembly of substantially larger constructs, but those required specialised conditions.
- Does Gibson Assembly leave a scar?
- No. Because the fragments are joined through homologous overlap sequences that you design yourself, the final construct contains exactly the sequence you specified, with no residual restriction site or linker. This is the main advantage over classical restriction cloning.
- Why did my Gibson Assembly fail?
- The most common causes are overlaps that are too short or too AT-rich to anneal at 50 °C, carryover of template plasmid into the assembly (which produces background colonies of the original vector), too much total DNA in the reaction, and repeated sequence within the construct causing fragments to anneal in the wrong position. Treating the PCR product with DpnI to destroy methylated template removes the most frequent source of background.
References
- Gibson DG, Young L, Chuang RY, Venter JC, Hutchison CA, Smith HO. Enzymatic assembly of DNA molecules up to several hundred kilobases. Nature Methods 6, 343–345 (2009). https://doi.org/10.1038/nmeth.1318
- New England Biolabs. NEBuilder HiFi DNA Assembly protocol and overlap design guidance. https://www.neb.com/en-us/applications/cloning-and-synthetic-biology/dna-assembly-and-cloning/gibson-assembly
Related
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