T4 DNA Ligase Guide: Restriction-Ligation Workflow from Vector Preparation to Transformation

Restriction Digestion + Ligation is the most classic and widely used technical route in molecular cloning. However, from double-digestion strategies and vector dephosphorylation to ligation system optimization, every step hides subtle details that influence positive cloning rates. Centered around Yeasen's Hieff™ Gold T4 DNA Ligase (Cat#10300ES), this guide outlines the complete operational workflow from vector preparation to obtaining clones.

1. Double Digestion: The Cornerstone of Successful Cloning

1.1 Restriction Enzyme Selection Strategy

1) Prioritize two enzymes that produce distinct protruding ends (e.g., EcoRI + HindIII), avoiding isoschizomers or compatible enzymes that generate identical sticky ends (e.g., BamHI + BglII), which can cause vector self-ligation.
2) Confirm buffer compatibility between the two restriction enzymes. Prioritize enzyme pairs that utilize the same buffer to reduce intermediate purification steps. Yeasen's FuniCut™ series restriction endonucleases share a single universal digestion buffer, greatly streamlining the digestion reaction system.
3) Selection of Multiple Cloning Sites (MCS): Ensure digestion does not disrupt selection markers on the vector (antibiotic resistance, LacZ, etc.).

1.2 Digestion System Reference (50 µL System)

 

Digest at the optimal temperature for the restriction endonucleases for 15 min (plasmids), 15–30 min (PCR products), or 30–60 min (genomic DNA). Upon completion, it is recommended to run 2–3 µL on an agarose gel to verify complete digestion. Incomplete digestion of supercoiled plasmids is one of the most common sources of high self-ligation background.

1.3 Post-Digestion Purification

Purification of digested products is mandatory for two reasons: to remove excised small fragments (stuffer fragments) to prevent competitive religation into the vector; and to remove restriction enzymes to avoid interference with subsequent ligation reactions. It is recommended to use gel recovery (MolPure™ Fast Gel Extraction Kit, Cat#19101ES) or PCR purification columns (MolPure™ PCR Purification Kit, Cat#19106ES), finally dissolving in 20–30 µL of ddH₂O or TE buffer.

2. Vector Dephosphorylation: The Key Step to Reduce Background

If performing single digestion, or if positive rates remain suboptimal after double digestion, dephosphorylating the linearized vector is strongly recommended. Dephosphorylation removes 5'-phosphate groups from the vector, preventing self-ligation while retaining 3'-OH groups to accept foreign fragment ligation.
1) Recommended enzymes: Antarctic Phosphatase (AnP) (Cat#14511ES), which efficiently remove 5'-phosphates from DNA/RNA.
2) Procedure: Purified linearized vector + 1–2 µL AnP, incubate at 37°C for 15–60 min; then heat-inactivate at 75°C for 5 min or purify before direct use in subsequent experiments.

3. Ligation Reaction: The Core of T4 DNA Ligase Application

3.1 Insert:Vector Molar Ratio Calculation

Insert Amount Calculation Formula:
Insert (ng) = Vector (ng) × Insert length (bp) / Vector length (bp) × Molar Ratio
Example: 50 ng vector (3000 bp), ligating 500 bp insert at 3:1 ratio:
Insert = 50 × 500 / 3000 × 3 ≈ 25 ng

3.2 Ligation System Formulation (20 µL System)

 

【Note】: When ligating blunt-end vectors with DNA fragments, pre-dephosphorylate the vector (e.g., using Antarctic Phosphatase, Cat#14511ES) to prevent self-ligation. To enhance ligation efficiency, add 2 µL of 50% PEG 4000 per 20 µL reaction system.

3.3 Reaction Conditions

Ligate at 16°C for 1–4 hours (overnight recommended for maximum efficiency) or at room temperature (22–25°C) for 1–2 hours.

4. Transformation: The Final Step from Ligation Product to Clone

4.1 Chemical Transformation (Recommended)

1) Add the ligation product to 100 µL of competent cells (ligation product should not exceed 1/10 of the competent cell volume), flick gently to mix, and incubate on ice for 30 min.
2) Heat shock the centrifuge tube at 42°C for 90 sec (without shaking), then immediately place on ice for 2–3 min.
3) Add 900 µL of LB or SOC medium to the tube, and incubate with shaking at 37°C, 150 rpm for 45 min to allow cell recovery and expression of resistance genes.
4) Centrifuge at 2500 g for 5 min, discard 900 µL of supernatant, resuspend cells in the remaining medium, spread evenly on selective plates with correct resistance using a sterile spreader, allow the liquid to absorb, and incubate inverted at 37°C overnight.

【Note】: If using super-competent cells (transformation efficiency > 10⁸ cfu/μg), 100–200 µL of the incubated culture can be plated directly; remaining culture can be stored at 2–8°C and re-plated within 1 week.

4.2 Electroporation (If Required)

⚠ Ligation products must be purified first (using a PCR purification column or ethanol precipitation) to remove salts and PEG; otherwise, arcing will occur during electroporation, damaging cuvettes and severely reducing transformation efficiency. Dissolve the purified ligation product in 10 µL of ddH₂O, and use 1–2 µL for electroporation.

5. Key Precautions Quick Reference

1) Digestion Completeness: Supercoiled and linearized plasmids migrate differently on gels; verify complete digestion via gel electrophoresis before proceeding.
2) Post-Dephosphorylation Purification: Vectors treated with CIAP (10321ES) must be purified to prevent residual CIAP from interfering with ligation.
3) Vector Amount: 50–100 ng of vector per 10 µL ligation system is sufficient; avoid excess. Excess vector increases self-ligation background.
4) Ligase Amount: 10301ES concentration is 400 U/µL; routine ligation requires 0.5–1 µL, while blunt-end ligation can be increased to 1–2 µL.
5) Negative Control: Always include a 'vector self-ligation control' (vector only, no insert) to evaluate the vector self-ligation background.
6) Positive Control: If feasible, include a positive control (known successful vector + insert combination) to verify that the entire workflow functions properly.

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