BRAF Primer Design

About BRAF

The BRAF gene (B-Raf proto-oncogene) on chromosome 7q34 encodes a serine/threonine-protein kinase in the MAPK/ERK signaling pathway. The BRAF V600E mutation (c.1799T>A) is the most common activating mutation, found in ~50% of melanomas, ~10% of colorectal cancers, and ~45% of papillary thyroid carcinomas. BRAF spans ~190 kb with 18 coding exons.

NCBI Gene ID: 673 | RefSeq: NM_004333.6 | Genomic: NC_000007.14 (140719327-140924764)

BRAF Primer Design Challenges

• V600E hotspot in exon 15: The most common mutation site requires precise amplicon placement around codon 600
• GC-rich exon 15: Approximately 65% GC content around the V600E mutation site
• Large introns: Introns 8 and 10 span>20 kb, requiring careful intron-spanning primer design for cDNA applications
• Alternative splicing: Multiple BRAF transcripts (including truncated isoforms) require transcript-aware design
• Pseudogene interference: BRAF pseudogene (BRAFP1) shares partial sequence homology with exons 4–11

Recommended Primer Design Parameters for BRAF

Key SNPs to Avoid in Primer Binding Sites

When designing BRAF primers, avoid these clinically significant variants:

• rs113488022 (c.1799T>A, V600E) — Most common BRAF activating mutation in melanoma
• rs397516897 (c.1799_1801delTGA, V600_K601delinsE) — Exon 15 in-frame deletion-ins
• rs121913351 (c.1397G>T, G466V) — Exon 11 kinase domain variant
• rs121913370 (c.1742A>G, N581S) — Exon 15 mutation
• rs121913355 (c.1406G>C, G469A) — Exon 11 non-V600 mutation

Recommended Primer Sequences for BRAF — Engine-Designed on NM_004333.6

The three pairs below were produced by VigyanLLM's automatic primer design engine directly against the Homo sapiens BRAF RefSeq mRNA NM_004333.6 (6459 nt), under the engine's default constraints: 18–25 nt primers, Tm 57–72 °C (optimum 62 °C), GC 40–60%, and an 80–1500 bp amplicon (optimum 150 bp). Every oligo was then re-checked back against the accession — each forward primer matches the sense strand at its stated 1-based position and each reverse primer matches the reverse complement ending at the amplicon's final base (3 of 3 exact matches for this page).

Pair 1 leads with a forward/reverse Tm spread of 0.0 °C, no stable hairpin at 37 °C (ΔG ≥ 0.0 kcal·mol⁻¹ on either oligo), self-dimer Tm at most -29.7 °C, no cross-dimer signal, no pair warnings, and a Primer3 pair-quality score of 100.0/100; the suggested starting annealing temperature is 53.4 °C. Pairs 2 and 3 are alternates from the same run — compare their Tm, GC and product columns above against your chemistry (dye-based or probe), then confirm every candidate in silico and on a gel before use.

How to read this table: these are default whole-transcript designs — they demonstrate what the engine produces under standard constraints and are not positioned over the clinically relevant variants discussed below; to land an amplicon on a specific codon or repeat, design against that region deliberately. Thermodynamics come from Primer3's nearest-neighbor engine (SantaLucia 1998). Example output only: validate each candidate experimentally (gel sizing, efficiency series, melt-curve or probe check) before relying on it.

Design Guidance for BRAF Assays

BRAF is a serine/threonine kinase in the RAS–MAPK cascade. Most BRAF alterations are single codon-600 substitutions, of which V600E (c.1799T>A, exon 15) dominates in melanoma, colorectal, thyroid and other tumours, with a long tail of non-V600 variants in codons 600, 601 and the activation segment.

Two design notes. First, BRAF has a well-characterised processed pseudogene, BRAFP1, with extensive sequence homology to BRAF: a pair that fits the transcript perfectly can still amplify the pseudogene on genomic DNA, so an in-silico specificity check against genomic resources is essential for gDNA assays. Second, decide the readout before ordering — Sanger or amplicon sequencing wants the variant centred in a short exon-15 product, while an allele-specific (ARMS-style) reaction wants the discriminating base at the 3′ end of a dedicated primer. Keep products short for FFPE-derived DNA (the example pair is 182 bp; re-run with a tighter window if your template is degraded) and validate efficiency on a dilution series before using the assay quantitatively.

Treat these pairs as validated starting candidates, not finished assays: check the binding sites for common variants to avoid allele dropout, re-run specificity against your template type, optimise annealing by gradient around 53.4 °C, confirm a single expected band, and document everything (sequence, lot, efficiency, RefSeq) so the run is reproducible.

References

• NCBI Nucleotide — RefSeq NM_004333.6 (Homo sapiens BRAF mRNA).
• NCBI Gene — BRAF (Homo sapiens).
• SantaLucia J Jr. A unified view of polymer, dumbbell, and oligonucleotide DNA nearest-neighbor thermodynamics. Proc Natl Acad Sci USA 1998;95:1460–1465.
• Untergasser A, Cutcutache I, Koressaar T, et al. Primer3—new capabilities and interfaces. Nucleic Acids Res 2012;40:W115–W118.
• Ye J, Coulouris G, Zaretskaya I, et al. Primer-BLAST: a tool to design target-specific primers for polymerase chain reaction. Nucleic Acids Res 2009.
• Bustin SA, Benes V, Garson JA, et al. The MIQE guidelines: minimum information for publication of quantitative real-time PCR experiments. Clin Chem 2009;55:611–622.