Synonymous Mutation Designer
Introduce or remove a restriction site without changing the protein sequence.
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What it does
The synonymous mutation designer rewrites a coding DNA sequence so that a chosen restriction site appears or disappears, while every codon still encodes the same amino acid. It searches the CDS for the target motif, finds the synonymous codons that create or erase it, and reports each change with its codon position and residue. Molecular cloners use it to add a site for cloning or mutagenesis, or to delete a site that blocks an assembly, without touching the protein.
How it works
The tool reads the CDS in triplets and translates each codon to its amino acid. For each codon that overlaps the target motif, it lists the synonymous codons (those encoding the same residue) and picks one whose bases rewrite the motif. Because only synonymous changes are allowed, the protein never changes. It counts how many times the motif occurs in the original sequence and how many remain after editing; if a site cannot be removed by any synonymous path it reports the site as not removed and explains why. The search respects the genetic code, so stop codons are never altered.
Worked example
Take a 75 bp CDS starting ATG that contains the BamHI site GGATCC three times (spanning codons 5-6, 14-15 and 20-21). Setting the target to GGATCC, the tool proposes synonymous swaps such as GGA to GGT or TCC to TCT that break each GGATCC without changing Gly or Ser. It reports occurrences 3 and remaining 0 with the badge Site removed, and lists each mutated codon with its position. If one GGATCC sat inside a codon with no synonymous alternative, remaining would be 1 and the badge would read Site not removed.
When to use it
Use this when you must clone through a site that is missing, or must delete a site that conflicts with your assembly, without re-engineering the protein. The key pitfall is that a site may sit inside a codon that has no synonymous alternative, so it cannot be removed and the tool will say Site not removed. Silent changes can also disturb splicing signals, mRNA folding or codon pair bias, lowering expression even though the protein is identical. Always re-check the edited CDS for new stop codons, shifted restriction map and unwanted motifs before ordering.
FAQ
- What is a synonymous mutation?
- A synonymous mutation changes one or more bases of a codon without changing the amino acid it encodes, because the genetic code is degenerate. Here it is used on purpose: the tool edits only synonymous codons so the protein stays identical while a DNA motif such as a restriction site appears or disappears. The residue and its position are reported for every change so you can verify nothing in the protein changed.
- Can every restriction site be removed?
- No. A site can only be removed if at least one of its codons has a synonymous alternative that breaks the motif. The tool reports remaining sites and, if a site sits inside a codon with no synonymous option, marks it Site not removed and explains why. Sites spanning two codons often have more routes, but a site pinned in a Met or Trp codon, which have no synonyms, cannot be changed at all.
- Does the amino acid sequence change?
- No. The designer only allows synonymous codons, so every edited triplet still encodes the same residue, and stop codons are never touched. The protein sequence is byte-for-byte identical before and after. What can change is the DNA-level context: splicing signals, mRNA secondary structure and codon pair bias may shift, which sometimes alters expression even though the amino acid chain is unchanged.
- What site should I target?
- Use a motif of 4 or more bases, typically a known enzyme site such as BamHI GGATCC, EcoRI GAATTC or XhoI CTCGAG. Type it in the target field; the tool finds every occurrence in the CDS and proposes silent edits. Shorter motifs appear more often and may be harder to remove completely, while a 6 bp site usually gives a clean single change per occurrence.