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How can I locate the IIS6 region and the L1014F mutation in the full VGSC sequence?

I retrieved the full coding DNA sequence (CDS) of the voltage-gated sodium channel (VGSC) gene from NCBI. I need to design primers to detect the L1014F (kdr) mutation, which is reported to be located in Domain II, Segment 6 (IIS6) of the VGSC protein.

My confusion is: How can I determine where Domain II and Segment 6 are located within the full nucleotide or amino acid sequence? In other words, how do I identify the exact position of the IIS6 region and locate amino acid L1014 in my retrieved sequence so that I can design primers around this mutation?

What tools or databases are typically used to map VGSC structural domains (DI–DIV and S1–S6) onto a gene or protein sequence?

primer design
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updated by SeqBench • SeqBench • written by tahreem • tahreem

Based on the gene notation above it looks like you are referring to the Aedes egypti version of the gene. You can find the primer sequences for multiplex PCR for IIS6 in https://d-nb.info/1144375177/34

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written by GenoMax GenoMax

1 answer

The key thing to realize is that "L1014" is a protein coordinate, while your CDS is nucleotides, so the reliable path is to work in amino-acid space first, then map back.

  1. Translate your CDS in the correct frame and confirm it begins at the true start ATG (no 5' UTR offset). If your residue numbering comes out shifted by a constant, that offset is almost always the culprit.

  2. Anchor L1014 by conservation, not by raw count. The "1014" numbering originates from Musca domestica (para/VGSC, GenBank AAB47604). Align your translated protein to a well-annotated reference VGSC for your species (UniProt), or to that Musca sequence -- the kdr Leu sits in a highly conserved IIS6 stretch, so you'll land on the right residue even if your isoform has indels that shift the absolute position.

  3. Map the residue back to nucleotides. The codon for residue n spans CDS bases (3n-2) to (3n). So L1014 -> CDS bases 3040-3042. Verify that triplet actually encodes Leu (CTN / TTA / TTG) as a sanity check on your frame.

  4. For the DI-DIV / S1-S6 boundaries, don't trust fixed coordinates -- pull the transmembrane topology from the UniProt entry (Features -> Transmembrane) and project it onto your alignment. Segment boundaries drift between insect species.

  5. Then design primers flanking that codon so the mutable base sits well inside the amplicon (not under a primer's 3' end), with enough margin for clean Sanger reads across the site.

On the "what tools" part of your question: for the domain/topology mapping, UniProt (transmembrane features) plus any alignment viewer is all you need -- no VGSC-specific software required. For the mechanical translate -> locate the codon -> design primers chain, it helps to do it in one place. Disclosure: I work on SeqBench, a free browser workbench that chains exactly those steps (paste CDS -> Translate -> click the codon on the map -> Primers): https://seqbench.com/tools/primer-designer . Any translate + primer-design combo works just as well -- the alignment-anchoring step above is the part that actually pins the position; tooling only speeds up the mechanical bit.

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written by SeqBench • SeqBench

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