DNA to Protein Translator - Codon & Amino Acid Converter

A DNA to protein translator converts a DNA or RNA sequence into the chain of amino acids it encodes, using the standard genetic code. It reads the sequence three bases at a time and looks up each triplet in a fixed table of 64 codons.

How translation works

A gene is written in four letters: A, C, G and T (or U in RNA). Cells read these letters in non-overlapping groups of three called codons. Each codon stands for one amino acid, or for a stop signal that ends the chain.

This tool first cleans the input. It converts lowercase letters to uppercase, removes spaces, line breaks and digits, and changes every U to T, since RNA uracil pairs with the same codon as DNA thymine. It then rejects any character that is not A, C, G or T, such as ambiguity codes like N, so a sequence is never silently mistranslated.

The standard genetic code

The tool uses NCBI Translation Table 1, "The Standard Code", the genetic code used by most organisms including humans. It assigns each of the 64 possible codons to one of 20 amino acids or to a stop signal.

Three codons are stop codons: TAA, TAG and TGA. None of them code for an amino acid. When the tool reaches one, it ends translation there. The stop codon itself is not added to the protein, and any bases after it are ignored.

The codon ATG codes for the amino acid methionine (Met, M). In most organisms ATG also acts as the start codon, the codon where a ribosome begins reading a gene.

Reading frames

A DNA sequence can be read in three different ways, called reading frames, depending on which base you start counting from:

• Frame 1 starts at the first base.
• Frame 2 starts at the second base, skipping the first.
• Frame 3 starts at the third base, skipping the first two.

Shifting the frame by even one base changes every codon after it, so the same sequence can produce three completely different amino acid chains. Only one frame is usually the real coding frame of a gene.

Scanning to the first start codon

By default, the tool translates starting at the first base of the chosen frame, whatever codon that happens to be. This matches how the tool has always worked and is useful for translating a sequence you already know is in frame from position one.

The optional "scan to first start codon" setting changes where translation begins, not how it translates. When turned on, the tool looks along the chosen frame for the first ATG codon and starts translating from there, skipping over any bases before it. This mirrors how a ribosome finds the start of an open reading frame (ORF) rather than translating from an arbitrary point in a longer sequence. If no ATG exists in that frame, the tool reports that no start codon was found instead of guessing.

Turning the setting off returns to the original behavior: translation from the very start of the frame.

How to calculate a DNA to protein translation

1. Enter a DNA or RNA sequence. Spaces, line breaks, digits and FASTA-style characters are ignored automatically.
2. Choose a reading frame: 1, 2 or 3.
3. Optionally turn on "scan to first start codon" to begin at the first in-frame ATG instead of the start of the frame.
4. The tool reads the sequence three bases at a time, looks up each codon in the standard genetic code, and stops at the first stop codon.
5. The result is the protein sequence, written as one-letter amino acid codes, along with a codon-by-codon breakdown.

Worked example

Sequence: ATGGCCTAA, reading frame 1, start-codon scanning off.

The protein is MA. Translation stops at TAA, so nothing after it is read.

Now take a longer sequence, CCCATGGCCTAA, in frame 1. With scanning off, the tool reads from the very first base: CCC (Pro), ATG (Met), GCC (Ala), then TAA (stop), giving the protein PMA. With scanning turned on, the tool skips CCC, starts at the first ATG, and reads ATG (Met), GCC (Ala), then TAA (stop), giving the protein MA. Both are correct outputs of the same sequence; they answer different questions, one reading everything in the frame, the other reading only the open reading frame that starts at ATG.

Frequently asked questions

What is a codon?

A codon is a group of three DNA or RNA bases. Each of the 64 possible codons stands for one amino acid or for a stop signal, based on the standard genetic code.

Why does translation stop at a stop codon?

TAA, TAG and TGA do not code for an amino acid. They are stop signals. A ribosome reading a real gene releases the finished protein chain at that point, so the tool does the same and ignores any bases after it.

What is a reading frame, and why does it matter?

It is the starting point used to split a sequence into codons. Starting one or two bases later changes every codon that follows, so the same DNA can be read three different ways, only one of which is usually the real coding sequence.

What does "scan to first start codon" change?

It changes where translation begins, not the genetic code used. With it on, the tool skips ahead in the chosen frame to the first ATG and translates from there, the way a ribosome starts at a start codon. With it off, translation begins at the very first base of the frame.

Can I paste an RNA sequence?

Yes. The tool treats U the same as T, since RNA uracil and DNA thymine pair with the same codon meaning. Uppercase and lowercase letters are both accepted.

What happens if my sequence has letters other than A, C, G, T or U?

The tool flags the invalid characters and does not translate the sequence. This includes ambiguity codes such as N, which are common in low-quality sequencing data but are not valid inputs to translation.

What if the sequence length is not a multiple of three?

The tool translates every complete codon it can and reports the leftover one or two bases separately, without guessing what they might encode.