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Reference information for researchers and lab staff. It is not a handling protocol or safety instruction.
Short answer: what is puromycin?
Puromycin is an aminonucleoside antibiotic from the bacterium Streptomyces alboniger. It stops protein synthesis by causing premature chain termination on the ribosome. Because it is toxic to both prokaryotic and eukaryotic cells, labs use it as a selective agent: only cells carrying a resistance gene survive. The right concentration is found empirically for each cell line with a kill curve.
Definition and scope
PubChem (compound record CID 439530) describes puromycin as an aminonucleoside antibiotic derived from Streptomyces alboniger that causes premature chain termination during translation at the ribosome, and classes it as a protein synthesis inhibitor. Its molecular formula is C22H29N7O5 and PubChem lists a computed molecular weight of 471.5 g/mol. PubChem also notes its use as a selective agent in laboratory cell cultures.
In practice the word covers three different things that are easy to confuse: the compound itself, the enzyme that inactivates it, and the experiment used to set a dose. The sections below keep them apart.
Mechanism of action
According to PubChem, puromycin is an analog of the 3′ terminal end of aminoacyl-tRNA. It incorporates itself into the growing polypeptide chain and causes its premature termination. The truncated chain is released, so the cell cannot complete the proteins it is making. That is why the compound is toxic to prokaryotic and eukaryotic cells alike, as PubChem records.
Puromycin structure and molecular weight
The structure is a nucleoside-like scaffold, which is what lets it mimic the end of an aminoacyl-tRNA. The deposited structure, the formula C22H29N7O5 and the computed 471.5 g/mol are on the PubChem record. The 471.5 figure belongs to the parent compound as drawn there. A supplied salt form has its own, higher formula weight, so use the weight printed on your lot’s label when you calculate a stock.
Is puromycin the same as puromycin dihydrochloride?
Not exactly. PubChem lists puromycin hydrochloride as a salt form whose active moiety is puromycin, so the biologically active part is the same compound. The two differ in formula weight because the salt carries counter-ions. Treat them as the same active agent but not as interchangeable on a mass basis: calculate molar amounts from the formula weight of the form you actually hold.
Puromycin resistance gene
UniProt entry P13249 describes puromycin N-acetyltransferase from Streptomyces alboniger, an enzyme that can acetylate puromycin, which leads to its inactivation. In cell engineering this resistance function is delivered on a vector, so transduced or transfected cells survive puromycin while untransduced cells die. UniProt describes the enzyme in the context of puromycin biosynthesis in the producing organism; the companion entry P42712 covers O-demethylpuromycin-O-methyltransferase from the same pathway. For how a selectable marker sits on a construct, see plasmid design, and for the delivery step see the lentiviral transduction protocol guide.
Puromycin kill curve and working concentration
What is the working concentration of puromycin?
There is no single value that suits every cell line. A 2026 workflow review in Molecules and Cells states that the minimal lethal concentration (MLC) of the selection antibiotic, typically puromycin or G418, must be empirically determined (Min, Kim and Lee, 2026). That determination is the kill curve.
How a kill curve is designed
The same review describes seeding the parental cells in multiwell plates and exposing them to a gradient of antibiotic concentrations. The medium is replaced every 2 to 3 days, the cells are incubated for 7 to 8 days, and the lowest concentration that causes complete cell death is taken as the MLC. Use cells that do not carry the resistance gene, since the point is to find the dose that kills cells without it.
Puromycin selection concentration and stock solution
Selection concentration is the output of your own kill curve, not a catalogue number. Stock concentration, solvent and storage vary by supplier and by salt form, so they belong in the supplier’s product data sheet and the safety data sheet (SDS) for your lot, not in a general reference. Record the lot, the form (free base or hydrochloride) and the formula weight in your lab notebook so the kill curve can be reproduced.
Compound, enzyme and assay at a glance
| Term | What it is | Source |
|---|---|---|
| Puromycin | Aminonucleoside antibiotic from S. alboniger; causes premature chain termination; toxic to prokaryotic and eukaryotic cells | PubChem CID 439530 |
| Puromycin hydrochloride | Salt form listed with puromycin as its active moiety | PubChem CID 439530 |
| Puromycin N-acetyltransferase | Enzyme that acetylates puromycin, leading to its inactivation | UniProt P13249 |
| Kill curve (MLC determination) | Gradient of concentrations on parental cells; lowest dose giving complete death over 7 to 8 days | Min, Kim and Lee, 2026 |
Where it matters for labs
Puromycin selection is a routine step when building stable cell lines, and it appears in pooled screens that read out gene expression, for example in Perturb-seq. Because the dose is cell-line specific, a kill curve is a documented prerequisite step, and the lot and salt form belong in the record. The 2026 workflow review frames the MLC as something to be determined per selection antibiotic and cell line.
Common misunderstandings
- Puromycin and the resistance gene are not the same thing. One is the antibiotic, the other is the enzyme (puromycin N-acetyltransferase) that inactivates it.
- A kill curve is not optional because a number exists elsewhere. The cited workflow treats the concentration as empirically determined.
- Puromycin is not selective in a biological sense. It is toxic to both prokaryotic and eukaryotic cells; selectivity comes from the resistance gene.
- The salt and free base are not mass-equivalent. Use the formula weight of the form you hold.
FAQ
What is puromycin?
An aminonucleoside antibiotic from Streptomyces alboniger that terminates translation prematurely and is used as a selective agent in cell culture (PubChem).
How toxic is puromycin?
PubChem states it is toxic to both prokaryotic and eukaryotic cells, which is the property exploited in selection. For hazard classification and handling, read the SDS supplied with your lot.
What is the molecular weight of puromycin?
PubChem lists a computed 471.5 g/mol for the parent compound (C22H29N7O5). Salt forms have a different formula weight.
What is a puromycin kill curve?
An experiment that exposes parental cells to a gradient of concentrations and identifies the lowest concentration producing complete cell death, as described by Min, Kim and Lee (2026).
Sources
- PubChem, Puromycin, CID 439530, pubchem.ncbi.nlm.nih.gov/compound/439530 (read 2026-11-08).
- UniProt, P13249, puromycin N-acetyltransferase, Streptomyces alboniger, uniprot.org/uniprotkb/P13249 (read 2026-11-08).
- Min C, Kim J, Lee G. Workflows for stable cell line generation. Mol Cells 2026;49(5):100345. PMC13053741 (read 2026-11-08).
