Methionine Codons — ATG
Methionine (Met, one-letter code M) is encoded by a single codon — ATG in DNA, AUG in RNA.
It is the only amino acid with a single codon, so there is no codon choice to make here — but there is still a usage question, which is how often this codon appears at all. The table below has it for eight organisms.
Methionine codon usage by organism
Each number is that codon's share of all methionine codons in that organism, so every column sums to 100%. The highest in each column is the preferred codon a codon optimizer would pick.
| DNA | RNA | E. coli | Human | Yeast | CHO | Pichia | Insect | Arabidopsis | Zebrafish |
|---|---|---|---|---|---|---|---|---|---|
| ATG | AUG | 100% | 100% | 100% | 100% | 100% | 100% | 100% | 100% |
Reference approximations derived from the Kazusa Codon Usage Database — the same tables the codon optimizer runs on. Verify against your own expression system for critical work.
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Frequently asked questions
Which codons code for methionine?
One codon: ATG in DNA, or AUG in RNA. Methionine is the only amino acid with a single codon.
What is the methionine one-letter code?
M, and the three-letter code is Met. Those are what the sequence tools on this site read and write — paste a protein in either alphabet and it is understood.
Where do these usage numbers come from?
They are reference approximations derived from the Kazusa Codon Usage Database and are the same tables the codon optimizer on this site runs on. For critical work, check them against your own expression system rather than treating any single table as definitive.
Codons for the other amino acids
Or go back to the full codon table for the codon-to-amino-acid direction.