How do I change the start coordinate for a simple protein sequence?
Create or Open a Protein Sequence

Create or open a protein sequence in SnapGene.
A single-domain protein does not require annotation with a feature.
Add a Translated Feature (Optional)

If the protein sequence does not include an appropriate feature, then select the region to be numbered and click Features → Add Feature.

Name the feature and set the appropriate feature "Type:" then click OK to add the feature.
Set the Translation Numbering

Select the feature (if present) then click View → Set Translation Numbering.

Enter a new start coordinate for the protein sequence, then click OK.

The amino acid sequence will now be numbered using the new start coordinate.