In Silico Restriction Digest in Seqqio: Cut Sites, Ends, and Fragment Maps
Use Seqqio to model a complete restriction digest, compare linear and circular topology, inspect fragment ends, and decide what still needs laboratory verification.
A recognition sequence alone does not tell you the final construct. You also need the cut geometry, whether a site crosses the circular origin, which fragments remain after every eligible cut, and whether the resulting ends are blunt or overhanging. Seqqio keeps those pieces in one record and exposes the method as Seqqio-RestrictionDigest-v1.
Start with the topology, not the enzyme list
Open Restriction Digest and choose Single sequence or FASTA batch. Paste or open concrete double-stranded DNA written with A, C, G, and T. Then set the topology for the records you are testing.
| Input model | What Seqqio evaluates | Fragment consequence |
|---|---|---|
| Linear | Sites contained within the sequence | n distinct cuts normally create n + 1 fragments |
| Circular | Sites within the sequence and sites spanning the displayed origin | n distinct cuts create n fragments when at least one cut exists |
| Circular, no selected cut | The molecule remains uncut in this ideal model | One circular fragment is retained |
The built-in example is useful for learning this distinction. It loads synthetic constructs, selects circular DNA, and restores the default enzyme set. One example deliberately places an EcoRI site across the origin; another is an uncut control for EcoRI, BamHI, and HindIII. These are software controls, not biological vectors or experimentally characterized samples.
Select enzymes and read the cut geometry
Select one or more entries from Seqqio's named catalog, then run the digest. The current catalog contains 229 named enzymes. It is a curated application catalog rather than a claim to reproduce the whole REBASE database. Custom one-pair definitions can be added locally when you need a recognition and cleavage pattern that is not present.
For each hit, separate the recognition interval from the cut positions. Type IIS enzymes make that distinction especially important because they recognize an asymmetric motif and cut outside it. The NEB Type IIS table shows the same outside-the-site notation for enzymes such as BsaI and FokI.
| Result | Question it answers |
|---|---|
| Recognition site and orientation | Where and on which orientation did the motif match? |
| Top- and bottom-strand cuts | Are the cleavage coordinates the same or offset? |
| End type and overhang | Is the end blunt, 5-prime overhanging, or 3-prime overhanging? |
| Fragment interval and length | Which sequence belongs to each complete-digest fragment? |
| Origin-spanning flag | Does a circular feature cross the displayed coordinate origin? |
Check the complete fragment map
Inspect the fragment list after the site table. For a linear record, confirm that the ordered fragment lengths sum to the input length. For a circular record, also inspect any fragment marked as wrapping the origin. If two selected enzymes cut at the same phosphodiester bonds, the map may contain multiple site annotations but only one physical boundary; read the distinct cut boundaries rather than counting labels.
Save the complete report and sequence exports when the map will inform another step. The application retains record identity, settings, enzyme definitions, and fragment provenance, which makes the analysis easier to review than a copied list of fragment sizes. The Biopython restriction-analysis cookbook provides an independent reference for complete linear and circular digest concepts.
Know what the model does not predict
Seqqio models an ideal complete digest. It does not simulate partial digestion, star activity, methylation sensitivity, competing sites, reaction buffer, enzyme dose, incubation time, ligation efficiency, or migration on a gel. It also does not establish that a recognition site will be accessible in a particular DNA preparation.
Before moving to the bench, check the current supplier protocol for every enzyme. Sequence context and distance from a DNA end can affect cleavage; NEB publishes enzyme-specific guidance for cleavage near fragment ends. Use the Seqqio map to define the proposed fragments, then use experimental documentation to choose actual conditions.
When this workflow is a good fit
Restriction Digest is a practical fit when you need a visual, traceable answer for a small construct or a FASTA batch: teaching cut geometry, checking a cloning plan, reviewing origin-spanning sites, or handing fragments into another sequence task. It is not a replacement for laboratory validation or a full enzyme-vendor database.
Restriction Digest is one of 39 applications in Seqqio 0.1.0 for Windows 64-bit. The Seqqio workspace overview explains the shared history, batch, and export model. The complete toolkit is offered as a US$99 one-time purchase with no activation key.
References
- New England Biolabs. Type IIS Restriction Enzymes NEB selection chart Recognition sequences, outside-the-site cleavage notation, overhang lengths, and enzyme-specific attributes.
- Biopython contributors. Restriction analysis Biopython Cookbook Independent reference for recognition analysis and complete digests of linear and circular DNA.
- New England Biolabs. Cleavage Close to the End of DNA Fragments NEB usage guidelines Laboratory guidance showing that cleavage near a DNA end is enzyme and context dependent.