Restriction Digest Clone Verification: An Implementation Checklist

An implementation checklist for verifying a clone by restriction digest is a pass/fail gel, not a favorite enzyme. A clone is digest-verified only when the photograph matches a band table you wrote before the tube was set up. Unexpected bands are failures until they have a named cause. Pretty smears are not close enough.

What Must Be Written Before the Tube

Inputs are the intended map, the plausible wrong maps — empty vector, inverted insert, dropped part — and the enzymes already chosen to distinguish them. Enzyme choice is the diagnostic-enzyme page. One-tube versus stepwise is the double-digest strategy page. This page runs the check.

Addgene’s diagnostic-digest protocol states the job: cut the plasmid into predicted pieces and read the pattern. Write those sizes down. If you cannot, you are not ready to pipette.

Steps: Digest, Then Gel

1. Confirm DNA amount. Addgene’s digest protocol treats about 500 ng as a typical diagnostic load and 1–2 hours as a typical diagnostic incubation. Those are heuristics. The manufacturer’s unit definition wins.
2. Use the recommended buffer for the enzyme or enzyme pair you already chose. Do not invent a third buffer to save a tube; that decision lives on the strategy sibling.
3. Incubate at the specified temperature. Diagnostic digests are often shorter than cloning digests. Overnight is not automatically better.
4. Load a ladder and, if you have it, a known backbone or uncut control. Skip lanes so bands can be read. An uncut control tells you whether the digest happened at all. A known backbone tells you whether the empty-vector pattern is the one you predicted.
5. Photograph the gel against the written table. Name every band or name the failure. A photo without the table is a souvenir, not a verification record.

Expected Result and Verification

Expected result: every predicted band is present, no unexplained extras, and the wrong-clone patterns are absent. If the job was orientation, the off-center pair matches the intended orientation and not the invert. Verification: a second person can match the photo to the table without hearing the story. “Looks right” is not verification. Write the agarose percentage and the ladder identity on the same sheet as the sizes. A table that cannot be found next to the photo is not a record.

When the Digest Is Not Enough

Addgene also recommends sequencing key regions when you need identity the gel cannot see. Point mutations, tiny scars, and some assembly errors do not move a band. Extra bands may be star activity, incomplete cuts, or enzyme still bound to DNA — NEB’s troubleshooting guide lists those causes. A named cause is a reason to repeat the digest. It is not a pass. If the extra band matches a plausible wrong clone, treat it as that clone until sequencing or a second digest says otherwise. Do not call star activity first because it is a kinder story.

This Checklist Is Not the Build Path

The restriction-cloning build lives on its own checklist. Unique sites as a concept live on the uniqueness page. After the band table is written, a map such as ZettaGene can simulate restriction-enzyme digestion. Official copy documents that simulation. It does not score the gel. The takeaway is the written table — and the refusal to treat a pretty digest as a sequence. Simulation can tell you what the intended file should look like. Only the photograph tells you what the colony actually was.

Frequently Asked Questions

How do you know a restriction-digest verification passed?

The gel matches the band table written before the tube. Unexplained extras are a fail.

Can a clean digest replace sequencing of the junction?

Not for changes the digest cannot see. Use the digest to reject wrong clones; sequence when the mutation or scar is smaller than a band shift.