Key takeaways
- Sanger reads ~700–1,000 bases from each primer. A 6–10 kb plasmid needs many reactions to cover it fully.
- Whole-plasmid long-read sequencing reads the complete construct in one sample, with no primers, including the backbone.
- Whole-plasmid data catches the surprises: unexpected mutations, rearrangements, deletions and mixed clones.
- Use Sanger when you only need to check one junction or mutation, or to confirm a single critical base.
Why verify the whole plasmid?
Cloning, mutagenesis and propagation in E. coli can all introduce changes you weren't looking for: a point mutation in the promoter, a deletion between repeated elements, a backbone rearrangement or a duplicated insert. If you only sequence across the insert, these changes go unnoticed until an experiment fails. Verifying the full sequence before a construct goes into cells, animals or a manufacturing process removes that risk.
Option 1: Sanger primer walking
Sanger sequencing reads from a primer. To cover a whole plasmid you need a series of primers spaced along it, plus reads in both directions for confidence. For a typical 6–10 kb plasmid, that means many reactions and many primers, and gaps can remain where primers fail or the template is difficult (GC-rich regions, repeats, hairpins).
Sanger is still ideal when:
- you only need to confirm an insert junction or a site-directed mutation,
- you want to confirm a single critical base found by another method,
- you are screening many colonies for the presence of an insert.
Option 2: Whole-plasmid long-read sequencing
Here the plasmid is read end to end on a long-read platform. Many reads of the full molecule are combined into a consensus sequence of the entire construct, typically with read-level data so you can see the evidence behind each base.
What you get:
- the complete sequence, insert and backbone, with no primer design,
- detection of insertions, deletions and rearrangements anywhere in the plasmid,
- an indication of mixed populations, such as two clones in one prep or a sub-population with a deletion,
- confirmation of the plasmid's actual size.
| Sanger primer walking | Whole-plasmid long-read | |
|---|---|---|
| Coverage | Regions next to your primers | The entire plasmid |
| Primers needed | Yes, several per plasmid | No |
| Reactions per plasmid | Many for a full plasmid | One sample |
| Rearrangements and large deletions | Easily missed | Detected |
| Mixed clones | Unreadable mixed traces | Often visible in the read data |
| Long homopolymer runs | Reads well | Can be harder; confirm critical bases with Sanger |
Long PCR amplicons work the same way
The same long-read approach can sequence full-length PCR products of several kilobases in a single read, with no assembly. This is useful for verifying long inserts, gene variants and edited loci. On the estimate page, choose "PCR / Amplicon" and enter your size range.
How to prepare your sample
- Start from a single colony. A mixed culture gives a mixed result.
- Purify with a standard miniprep kit and elute in water or a low-EDTA buffer.
- Measure the concentration, ideally with a fluorometric method such as Qubit.
- Send the volume and concentration shown on your order page. They depend on the size tier you choose.
- If your sample is not purified, add the DNA cleanup option when you order.
Our one-minute sample-prep videos show the whole process for plasmids and PCR amplicons.
Reading the results
Compare the consensus sequence with your expected map. Look first at the overall length, then at differences in the insert and regulatory elements, and finally at the backbone. Our free DNA Sequence Comparer aligns your result to your reference in the browser, lists the variants and draws a dot plot, so rearrangements stand out at a glance.
Frequently asked questions
What is whole plasmid sequencing?
A long-read method that sequences the entire circular plasmid, usually on Oxford Nanopore, and returns a consensus sequence of the full construct. No primers are needed and the backbone is covered as well as the insert.
Do I need to send primers for whole-plasmid sequencing?
No. The plasmid is fragmented or linearised and read end to end, so no sequencing primers are required. Primers are only needed for Sanger sequencing.
Can whole-plasmid sequencing detect a mixed population of plasmids?
Yes, often. Because individual molecules are read, a mixture of two clones or a sub-population with a deletion can show up in the read data, where Sanger would give an unreadable mixed trace.
Is whole-plasmid sequencing accurate enough to replace Sanger?
For most construct verification, yes: the consensus is built from many reads of each position. Long homopolymer stretches (runs of the same base) can be harder for nanopore data, so if a single base in such a region is critical, a targeted Sanger read is a good confirmation.
How should I prepare my plasmid?
Send purified plasmid DNA from a single clone, free of RNA and genomic DNA, at the concentration and volume shown on your order page. Our short sample-prep videos walk through it step by step.
