Restriction Digest Calculator (Master Mix & Star Activity)
Design bench-ready restriction endonuclease digestion recipes for single or double digests. Automatically calculates DNA volumes, enzyme units, water Q.S., and performs strict glycerol concentration checks to prevent star activity.
Restriction Digestion Setup
Bench Pipetting Recipe
| Component | Volume |
|---|---|
| Nuclease-free Water | 38.0 µL |
| 10X Digestion Buffer | 5.0 µL |
| DNA (1000 ng) | 5.0 µL |
| EcoRI-HF | 1.0 µL |
| BamHI-HF | 1.0 µL |
| Total Reaction Volume | 50.0 µL |
Incubate at 37°C for 30–60 minutes (or 15 min for High-Fidelity HF enzymes).
Restriction Digest Calculator Principles & Enzyme Cleavage Units
Restriction endonucleases recognize specific palindromic 4–8 base pair double-stranded DNA sequences and catalyze phosphodiester bond hydrolysis. One unit (1 U) of restriction enzyme is defined as the amount required to completely digest 1 µg of λ DNA in a 50 µL reaction volume in 60 minutes at 37°C.
Starting Enzyme Amount
Some protocols use 5–10 U per microgram of DNA as a starting estimate, but unit definitions and recommended amounts vary by product. Salt or ethanol carryover can affect the reaction. Follow the enzyme supplier’s instructions; this calculator cannot predict digestion completeness.
Double Digest Buffer Choice
A multi-enzyme buffer can simplify a double digest when both enzymes are compatible, but compatibility and activity depend on the specific products. Check the supplier’s compatibility data; sequential digestion or cleanup may be needed.
Virtual Agarose Gel Electrophoresis Simulation
Representative agarose gel electrophoresis (1.0% gel in 1X TAE) migration profiles: Uncut circular plasmids exhibit abnormal conformational mobility; single digestion resolves into a single linear band; double digestion separates the vector backbone from the excised insert.
Restriction Enzyme Recognition Sites and Ends
| Enzyme | Recognition Site | Overhang | Temp | Heat Inactivation | Star Activity Risk |
|---|---|---|---|---|---|
| EcoRI-HF® | G▼AATTC | 5′ overhang (AATT) | 37°C | 65°C, 20 min | Low (HF formulation) |
| BamHI-HF® | G▼GATCC | 5′ overhang (GATC) | 37°C | Check product instructions | Low (at ≤5% glycerol) |
| HindIII-HF® | A▼AGCTT | 5′ overhang (AGCT) | 37°C | 80°C, 20 min | Low |
| XhoI | C▼TCGAG | 5′ overhang (TCGA) | 37°C | 65°C, 20 min | Moderate (check for long incubations) |
| NdeI | CA▼TATG | 5′ overhang (TA) | 37°C | 65°C, 20 min | Recognition site contains the ATG start codon |
| NotI-HF® | GC▼GGCCGC | 5′ overhang (GGCC) | 37°C | 65°C, 20 min | 8 bp recognition site |
| SmaI | CCC▼GGG | Blunt end | 25°C | 65°C, 20 min | Check product instructions |
Reaction temperature, heat-inactivation conditions, and star-activity behavior can vary by supplier and product formulation. Check the current instructions for the enzyme you use.
💡 Tip: If the restriction enzyme cannot be heat-inactivated under its product instructions and the next reaction is not compatible with carryover, consider DNA cleanup before ligation. Check the enzyme and ligation reagent instructions.
Preventing Star Activity in Restriction Enzyme Digestions
Star Activity occurs when a restriction endonuclease relaxes its sequence specificity, cleaving sequences similar but non-identical to its canonical recognition site.
Excess Glycerol (> 5%)
Enzyme stocks may contain glycerol. A high enzyme-stock fraction can affect the reaction, so follow the product instructions when setting up the reaction.
Over-incubation
Long incubations may increase nonspecific cleavage depending on the enzyme and conditions. Check the product instructions before extending the recommended reaction time.
Low Ionic Strength / High pH
Use a reaction buffer and water compatible with the enzyme, and follow the supplier’s recommended conditions. pH and Mg²⁺ concentration can affect enzyme activity.
Restriction Digest Calculator Worked Lab Example: Cloning Vector Linearization
Scenario: Cloning Vector Linearization (EcoRI-HF + XhoI)
You need to digest 1.5 µg of pET-28a plasmid (conc = 250 ng/µL) in a 50 µL reaction for directional cloning.
- 1. Vector DNA volume: 1500 ng / 250 ng/µL = 6.0 µL
- 2. 10X rCutSmart Buffer: 50 µL / 10 = 5.0 µL
- 3. EcoRI-HF (20 U/µL): 1.0 µL (20 U)
- 4. XhoI (20 U/µL): 1.0 µL (20 U)
- 5. Nuclease-free water: 50.0 − (6.0 + 5.0 + 1.0 + 1.0) = 37.0 µL
- QC: Enzyme volume = 2.0 µL in 50 µL = 4.0% total volume → 2.0% glycerol (≤ 5% threshold).
Frequently Asked Questions (FAQ)
How much restriction enzyme should I add per microgram of DNA?
The standard rule of thumb is 5 to 10 Units of enzyme per 1 µg of plasmid or genomic DNA for a 1-hour incubation. For rapid digestion with High-Fidelity (HF) enzymes, 1 µL (usually 20 U) digests 1 µg in 15 minutes.
Why must glycerol concentration remain below 5%?
Commercial enzymes are stored in 50% glycerol. When glycerol exceeds 5% in the final reaction, the enzyme's active site conformation changes, triggering star activity (relaxing sequence specificity and cutting off-target sites).
How do I choose buffers for double digestions?
Most modern recombinant and High-Fidelity enzymes (such as NEB rCutSmart or Thermo FastDigest) work at 100% activity in a single universal buffer, eliminating the need for sequential digests or buffer exchange.
When is heat inactivation preferred over column purification?
If the enzyme can be heat inactivated (e.g. 65°C or 80°C for 20 min) and the downstream reaction is compatible with the digest buffer, heat inactivation is preferred to avoid DNA column yield loss (~20–30%). Heat-resistant enzymes (like BamHI) require column clean-up.
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