Two Methods of DNA Cloning Explained
What DNA Cloning Actually Is
DNA cloning is the process of making identical copies of a DNA fragment. Scientists insert the fragment into a vector (usually a plasmid), then introduce that vector into a host organism like E. coli. The host replicates, and you end up with millions of copies of your original DNA.
Two methods dominate the field. The first is restriction enzyme cloning—the old-school workhorse. The second is Gateway cloning—a recombination-based system that Eli Lilly commercialized. Both get the job done. Neither is magic.
Method 1: Restriction Enzyme Cloning
This is the classic approach. You cut both your DNA fragment and your plasmid with the same restriction enzymes. The cut ends have sticky overhangs that match. You mix them together with DNA ligase, and the fragment slots into the plasmid like a puzzle piece.
How It Works
- Identify restriction sites flanking your insert
- Digest the plasmid and insert with matching enzymes
- Ligate using T4 DNA ligase
- Transform into competent E. coli
- Screen colonies via antibiotic selection and PCR
The Problems
Restriction sites have to exist where you want them. Sometimes they don't. You might need to add sites via PCR, which introduces errors. You can't easily swap fragments in and out without designing everything from scratch. It's iterative, slow, and prone to failure if your enzymes don't cooperate.
Multi-fragment assemblies are a nightmare. Each piece needs compatible ends. The more fragments you add, the more your efficiency drops.
When to Use It
Single insert. Simple constructs. When you don't have access to Gateway vectors. When your budget is tight and you have time to troubleshoot.
Method 2: Gateway Cloning
Gateway uses site-specific recombination instead of restriction enzymes. Two enzyme systems handle this: BP clonase recombinase (for inserting fragments into entry vectors) and LR clonase recombinase (for moving fragments from entry vectors into destination vectors).
The system relies on att recombination sites: attB, attP, attL, and attR. These sites are incompatible with each other in a specific way—BP reactions recombine attB with attP to create attL and attR, while LR reactions do the reverse.
How It Works
- PCR-amplify your gene with attB flanking primers
- Mix with a donor vector (contains attP sites) and BP clonase
- The PCR product recombines into the entry clone
- Mix entry clone with destination vector and LR clonase
- The gene moves into your final expression vector
The Advantages
Once your gene is in an entry vector, you can move it into any Gateway destination vector with a single LR reaction. Different promoters? Different tags? Different expression systems? Doesn't matter. The entry clone stays the same.
You can also do multi-fragment assemblies using attB1, attB2, attB3, and attB4 sites. Up to four fragments assemble in one reaction. Efficiency is decent if your fragments are sized correctly.
The Problems
Gateway vectors cost money. The clonase enzymes cost money. The entry vectors aren't free either. If you're cloning on a shoestring, this isn't your first choice.
The att sites add 25-26 base pairs to each end of your insert. For most applications, this doesn't matter. For some applications, it absolutely does.
Head-to-Head Comparison
| Feature | Restriction Cloning | Gateway Cloning |
|---|---|---|
| Cost | Low (enzymes only) | High (vectors + enzymes) |
| Flexibility | Limited by available sites | One entry, unlimited destinations |
| Multi-fragment assembly | Painful | Manageable (up to 4 fragments) |
| Speed | Slower (iterative optimization) | Faster (modular workflow) |
| Sequence scar | Usually minimal | 25-26 bp at each end |
| Learning curve | Steep (troubleshooting) | Moderate (standardized) |
Getting Started: Which Should You Pick?
Answer these questions:
- How many constructs do you need? If it's under five, restriction cloning probably works fine. If you're building a library or need dozens of variants, Gateway saves time.
- Do you need to swap between expression systems? If you're working across multiple systems (bacterial, yeast, mammalian), Gateway eliminates redundant cloning steps.
- What's your budget? Restriction cloning needs nothing beyond standard reagents. Gateway requires purchasing the system components.
If you choose restriction cloning: start with a high-quality plasmid map, pick enzymes that cut once in your vector and nowhere in your insert, and verify everything with sequencing.
If you choose Gateway: buy the entry vector that matches your downstream destination system, design your PCR primers with the correct attB sites, and follow the manufacturer's protocol for transformation—Gateway reactions transform with lower efficiency than standard ligation.
The Bottom Line
Restriction enzyme cloning is cheap and flexible if you're willing to work for it. Gateway cloning is expensive and standardized if you want reliability over control. There's no universal winner.
Most labs end up using both. Gateway for routine expression constructs, restriction cloning for anything that doesn't fit the Gateway framework. Pick the tool that matches your actual problem, not the one that sounds more sophisticated.