Restriction Cloning: From Map to Bench Without a Second Cut
An in-silico-to-bench restriction cloning checklist is a written restriction-ligation plan, not a colony count and not a multi-fragment method page. The outcome is a record a second person can read: unique sites, compatible ends, methylation risk, and expected diagnostic bands — on the expected construct — before anyone sets up a digest. This page walks that path. It does not run Gibson or Golden Gate, and it does not promise the later clone will work.
Outcome, Prerequisites, and Boundary
The outcome: a signed restriction-ligation plan. It names the cloning enzymes, whether ends need phosphatase, the Dam or Dcm risk, and the diagnostic band sizes. Colonies are not the outcome. A simulated cartoon without those numbers is not the outcome.
Prerequisites: insert and vector sequences, and an expected assembled product from a cloning planner. If the method is not restriction-ligation, stop. This page will not convert the plan to overlaps or Type IIS overhangs. Authority to freeze the digest is required; discovering an extra cut on the gel is more expensive than a table row.
The boundary: restriction-ligation only. The design-review workflow still owns the signed unique-site row before oligos are ordered. This page owns the ligation plan through diagnostic bands. It is not a wet-lab protocol replacement. Addgene's subcloning protocol still follows at the bench. A planned unique-site explainer in this series is not linked here because it is not yet public; uniqueness is defined in place below.
Build the Restriction-Ligation Plan in Order
Run the first four checks in order. Verification and rollback are their own sections; do not start the wet digest to discover an extra cut.
- Confirm unique sites. Choose enzymes that flank the insert and do not cut inside it, sit at the intended location on the recipient — usually the MCS — and do not cut elsewhere on that plasmid, and that set the insert in the correct orientation. Addgene's subcloning protocol writes those four tests in those words. A familiar enzyme name is not enough. SnapGene's restriction-cloning guide puts the first tip the same way: choose a combination that cuts uniquely in the insert and the vector. Checkpoint: the reviewer can list each cloning enzyme and show a count of one where the plan requires one cut.
- Name the ends. Two different enzymes that leave non-compatible overhangs force directional cloning and lower empty-vector background. A single enzyme, or enzymes with compatible or blunt ends, needs phosphatase on the recipient and a later orientation digest. Write which case you are in. SnapGene notes that most enzymes also need four to six bases adjacent to the recognition site for efficient cleavage. Checkpoint: the plan says directional or single-enzyme, names the overhangs, and states whether phosphatase is required.
- Check methylation before the enzyme is committed. Dam methylates adenine in GATC. Dcm methylates the internal cytosine in CCAGG and CCTGG. Standard cloning strains are usually Dam+ Dcm+. Addgene's digest protocol tells readers that if the enzyme did not cut, they should check methylation sensitivity — plasmids from Dam- or Dcm-positive strains can resist cleavage. Do that check on paper, not after an empty gel. If the committed enzyme is blocked, change enzyme or grow the plasmid in a dam-/dcm- strain. Checkpoint: each cloning enzyme has a written note: clear, blocked, or grow in dam-/dcm-.
- Write the diagnostic digest before wet work. Name the enzymes and the expected band sizes that distinguish insert-plus-vector from empty backbone, and that distinguish orientation when ends were compatible or single-enzyme. Addgene's finished-plasmid check digests 100–300 ng with the cloning enzymes and expects a vector-sized band and an insert-sized band. A single unique cutter that only linearizes does not do that job. Checkpoint: expected sizes are written on the plan, not invented after colonies appear.
Once those four gates are executable on any annotated map, a restriction simulator is one way to see the cuts before the bench. After the plan is written, ZettaGene is one example of a place to simulate restriction enzyme digestion and to keep track of details such as DNA methylation. Use it for that job on this page. Do not treat the cartoon as a clone, and do not read this paragraph as Golden Gate coverage.
Stage, Output, and Completion Criteria
A researcher should be able to mark progress without a gel photo. Running the digest is not a phase on this page.
| Stage | Output | Done when |
|---|---|---|
| Unique sites | Named enzymes with cut counts on insert and recipient | Each planned unique site occurs once; the insert is not cut internally |
| Ends | Overhang names; directional or single-enzyme; phosphatase yes/no | A second person can state orientation control from the plan |
| Methylation | Dam/Dcm note per committed enzyme | No committed enzyme is left as "not checked" |
| Diagnostic bands | Enzymes and expected sizes, including orientation if needed | The pattern distinguishes insert from empty backbone on paper |
| Simulation (optional) | Restriction digest viewed on the expected map | The cartoon matches the written sizes; it does not replace them |
| Rollback | Written freeze for extra site, bad ends, block, or unreadable digest | A named owner exists for the first fail |
If a row is incomplete, the plan is incomplete. Do not advance to the bench on a skipped row.
Expected Result and Verification
The plan is ready for the bench when two tests pass on paper — not when a simulator draws a clean map.
Reconstruction test. Hand the plan to a person who did not design it. They must state the cloning enzymes, whether ends need phosphatase, the methylation note, and the expected diagnostic bands, without asking the designer.
Expected-pattern test. The diagnostic sizes exist on the record before the first digest. If the only number on the page is "will linearize," the diagnostic row failed.
Colonies, a successful ligation, or a later Sanger trace are not this verification. Those tests compare a molecule to this approved plan. They cannot rescue a plan nobody signed. This page does not guarantee experimental success.
Failure Paths and Rollback
- A planned unique site is duplicated. Symptom: the assembled map shows a second cut inside the insert or elsewhere on the recipient. Recovery: freeze the digest, redesign or retarget the sites, and re-run the unique-site checkpoint. Do not discover the extra band on the gel.
- Ends are compatible and phosphatase was skipped. Symptom: the plan says "single enzyme" or "compatible overhangs" with no phosphatase line. Recovery: add phosphatase and an orientation digest, or switch to two non-compatible ends, then re-sign.
- Methylation would block a committed enzyme. Symptom: the site overlaps Dam or Dcm and the note is empty, or the enzyme is famous for failing on Dam+ DNA. Recovery: change enzyme or strain before the digest. Do not debug it as a bad tube.
- The diagnostic pattern cannot be stated. Symptom: no sizes, or a single unique cut that cannot tell insert from empty vector. Recovery: choose enzymes that produce a readable pattern, write the sizes, and only then release the bench.
A freeze here is a planning fail. It is not a claim the reaction would have produced zero colonies.
Frequently Asked Questions
When is a restriction site unique enough to clone with?
The enzyme must not cut inside the insert and must cut the recipient only where you intend. A second site on the assembled construct fails the unique-site row.
Why check methylation before committing to an enzyme?
Dam or Dcm methylation from a standard cloning strain can block an otherwise perfect site. If the committed enzyme is sensitive, change enzyme or strain before the digest, not after an empty gel.
What should a diagnostic digest prove that a unique cutter does not?
A readable band pattern for insert presence and, when ends were compatible or single-enzyme, orientation. One unique cutter confirms length and little else.
Does this checklist cover Gibson or Golden Gate?
No. This page is restriction-ligation: unique sites, ends, methylation, diagnostic digest. Gibson overlaps and Type IIS overhangs are a different plan.
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