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Short answer
A plasmid map is a diagram of a plasmid’s circular DNA that labels its features, such as antibiotic resistance genes, promoters, origins and tags, and marks where restriction enzymes cut. Repositories such as Addgene generate the map from the plasmid’s sequence plus feature annotations, so the map is only as good as the sequence behind it.
Definition and scope
The National Human Genome Research Institute describes a plasmid as “a small circular DNA molecule found in bacteria and some other microscopic organisms.” Plasmids are physically separate from chromosomal DNA and replicate independently. They often carry a few genes, including antibiotic resistance genes, and genes inserted by recombinant DNA methods are copied when the plasmid replicates.
A plasmid map turns that circular molecule into something a person can read: a ring with labelled features, plus lists of positions and enzyme sites. This page covers how to read a map, how a repository map is produced, and what to check before relying on one. It does not give cloning or digestion protocols; for the bench side see setting up a restriction enzyme digest.
What a plasmid map shows
Addgene’s description of its SnapGene-powered maps gives a clear picture of what a modern map contains:
- Features are labelled directly on the map. Addgene’s examples are antibiotic resistance genes, selectable markers, promoters, origins, tags and certain open reading frames (ORFs).
- A feature table lists each feature’s name, location, size, direction, type and the colour used on the map.
- A restriction enzyme table lists the enzymes that cut the given sequence.
Addgene also notes that its feature library “eliminates many of the extraneous ORFs”, so the ORFs you see labelled are a curated selection, not every possible reading frame in the sequence.
Reading features and restriction sites
How to read plasmid maps
Start with the feature table rather than the picture. The table gives locations and sizes as numbers, and the direction of each feature. Then match each colour on the ring to its table row. Finally, look at the enzyme list: each enzyme on the map or in the table is there because it cuts the displayed sequence.
Plasmid restriction map and restriction mapping
On Addgene’s pages the restriction information sits in its own table with filters for single, dual and 3+ cutters, so you can narrow the list to enzymes that cut the sequence once, twice or more often. Since the 2017 update the tool also includes Type IIS enzymes commonly used for Golden Gate cloning. Treat the table as a list of enzymes that cut this sequence, not as a recommendation of which to use. For a worked bench context, see the digest setup guide, which also covers why a stale map causes confusing gel results.
Where the map comes from
A map is not hand-drawn art. Addgene states: “We auto-generate a plasmid map based off of the plasmid sequence and feature information given by our depositors.” The sequence itself comes from depositors and from Addgene’s own sequencing. Sequences are provided in FASTA format, and depositors can upload GenBank files, which carry annotations as well as sequence. GenBank files uploaded by depositors are found in the Resource Information section of the plasmid page, and Addgene’s sequence page lets you download an annotated GenBank file or a SnapGene file.
So “plasmid mapping”, in a repository workflow, means producing this annotated view from sequence data. If you build your own maps in desktop software, compare the options in SnapGene vs Benchling.
Feature map and restriction map compared
| Question | Feature view | Restriction view |
|---|---|---|
| What it lists | Names, locations, sizes, colours, direction and types of features | Restriction enzymes that cut the given sequence |
| How to narrow it | Features are labelled directly on the map | Filters for single, dual and 3+ cutters |
| Source in Addgene’s description | Feature information supplied by depositors, with a feature library applied | A table of enzymes that cut the given sequence, including Type IIS enzymes |
Checklist before relying on a map
- Who generated the map? A repository map is auto-generated from the sequence and the depositor’s feature information, so check that the annotations came from the depositor or a stated library.
- Where did the sequence come from? Addgene draws on sequence information from depositors and its own sequencing results. Know which one you are looking at.
- Is a sequence file available? FASTA and annotated GenBank files are offered. A file lets you re-open the map in your own software instead of trusting a picture.
- What is the backbone? Addgene defines the backbone as “the starting vector that the depositing lab modified to create their new plasmid.” Record it, because it tells you what the plasmid was derived from.
- Which enzymes are shown? Check whether the list is filtered to single cutters before assuming an enzyme cuts only once.
If you plan to move a plasmid into cells, competent cells and E. coli protein expression cover the next step.
Common misunderstandings
“The map is the plasmid.”
The map is a view generated from sequence and annotation data. If the sequence or annotations change, the map changes.
“Every labelled feature is the full story.”
Feature libraries select what to show; Addgene’s removes many extraneous ORFs. A missing label is not proof that nothing is there.
“A restriction map and a feature map are the same thing.”
They answer different questions: what the sequence contains versus where enzymes cut it. Addgene presents them as separate tables.
FAQ
How do I read a plasmid map?
Use the feature table for names, positions, sizes and directions, match colours to the ring, then check the restriction table filtered by cutter number.
What is a plasmid restriction map?
It is the list or diagram of restriction enzymes that cut a plasmid’s sequence, which Addgene lets you filter into single, dual and 3+ cutters.
What is plasmid mapping?
It is producing an annotated view of a plasmid from its sequence and feature information, as Addgene does automatically for deposited plasmids.
Where can I get the sequence behind a map?
Addgene provides sequences in FASTA and offers annotated GenBank or SnapGene files for download on its sequence page.
Sources
- National Human Genome Research Institute, Genetics glossary: Plasmid. Checked 2026-10-29.
- Addgene blog, Improved Plasmid Maps Powered by SnapGene (published 29 June 2017). Checked 2026-10-29.
- Addgene blog, Anatomy of a Plasmid Page at Addgene. Checked 2026-10-29.
