Primer Design

Primers can be designed directly against the sequences annotated in CnidoSite, or against a sequence you paste in. Design is performed by primer3 (version 2.6.1) running on this server — your sequence is not sent to any third-party website. For reference, the primers released with this database were designed with an optimal melting temperature of 60°C (58–62 °C), an optimal primer length of 20 bp (18–24 bp), and a GC content between 40% and 60%, with self-complementarity restricted to limit primer-dimer formation; that parameter set is the CnidoSite published protocol preset below.

Template taken from CnidoSite: OS493_037827-T1 (OS493_037827-T1), 2,736 bp.
Template

Two ways to supply a template: pick a species and a gene / transcript ID, or paste your own sequence. If the gene ID is found it is used; the pasted sequence is used otherwise. A template must be at least 30 bp.

Load example sequence
Primer parameters
Advanced parameters (any field left empty keeps the preset value)

A value that is not a number is ignored. The product size range is applied only when both of its fields are filled in and the maximum is at least the minimum.

Melting temperature
Primer length and GC content
Product and output
Self-complementarity and probe
Download TSV
Design results sorted by primer3 penalty, lowest first

Template 2,736 bp · parameter preset CnidoSite published protocol (Tm 60 [58-62] °C, 20 [18-24] bp, GC 40-60%) · 5 primer pairs returned.

Pair Left primer (5'→3') Position Len Tm (°C) GC (%) Right primer (5'→3') Position Len Tm (°C) GC (%) Product (bp) Penalty
1 AAGAAACGTACCGCTGAGCT 205–224 20 59.683 50.000 TCATCCTCTAGCTCAGCGGT 382–401 20 60.106 55.000 197 0.424
2 GAGCTAGAGGATGAACGGCG 2083–2102 20 60.318 60.000 TCATCCTCTAGCTCAGCGGT 2233–2252 20 60.106 55.000 170 0.425
3 GAGCTAGAGGATGAACGGCG 1999–2018 20 60.318 60.000 TCATCCTCTAGCTCAGCGGT 2233–2252 20 60.106 55.000 254 0.425
4 GAGCTAGAGGATGAACGGCG 1753–1772 20 60.318 60.000 TCATCCTCTAGCTCAGCGGT 1921–1940 20 60.106 55.000 188 0.425
5 GAGCTAGAGGATGAACGGCG 1681–1700 20 60.318 60.000 TCATCCTCTAGCTCAGCGGT 1921–1940 20 60.106 55.000 260 0.425
Primer map pair 1 (lowest penalty) · product 197 bp at template position 205–401 · the template track shows a 1,500 bp window of the 2,736 bp template — the blue segment on the top bar is where that window sits, and every scale is in template coordinates · the two tracks are drawn at different scales

Left primer — binds the template strand as listed (5′→3′)Right primer — its reverse complement binds hereProductWindow drawn in the template track

whole templatethe 1,500 bp drawn in the track below · template 1–1,500 of 2,736Template1,500 bp windowproduct 197 bp · template 205–401product 197 bpleft primer, template 205–224right primer anneals here, template 382–40113767511,1251,500Amplicon197 bpleft primer AAGAAACGTACCGCTGAGCT · 5′→3′right primer TCATCCTCTAGCTCAGCGGT · its reverse complement binds the template strandinterior 157 bp205254303352401
Left primer
AAGAAACGTACCGCTGAGCT
template 205–224 · 20 bp · Tm 59.683 °C · GC 50.000 %
Right primer
TCATCCTCTAGCTCAGCGGT
template 382–401 · 20 bp · Tm 60.106 °C · GC 55.000 %

Amplicon sequence (5′→3′ on the template strand, 197 bp) — blue is the left primer, red is where the right primer anneals. Copy from here to order or to check a base by eye.

AAGAAACGTACCGCTGAGCTAGAGGATGAACGTCGACAAAAGAACTGTCTCCAAGATAAAGTGAAGGATAAAGAAGAAACATTTAAGAAACTTACCTCTGAGCTAGAGGATGAACGGCGACAAAAGAAAGATCTCCAAGATAAAGTGAAGGATAAAGAAAAAACATTTAAGAAACTTACCGCTGAGCTAGAGGATGA

The right primer is listed as its own 5'→3' sequence; what anneals to the template strand shown here is its reverse complement, so the highlighted stretch is complementary to the listed sequence. That is expected.

How to read this table. Position is a 1-based interval on the template, and both primers use the same convention: it is the stretch the primer occupies on the template strand (for the left primer, starting at its 5’ end; for the right primer, the region it anneals to, i.e. where the reverse complement of the listed sequence sits on the template). The two coordinates in a row can therefore be subtracted directly, and the amplicon view above marks both of them so you can check them by eye. Penalty is primer3’s weighted sum of the deviations from your constraints — lower is better, and the pairs are returned in that order. Tm is computed by primer3 from the SantaLucia thermodynamic parameters at the salt and primer concentrations in effect. The primer sequences themselves are 5’→3′ and can be ordered as they stand; the right primer anneals to the template as its reverse complement.

Specificity has not been assessed. This page only designs primers; it does not check whether they also anneal elsewhere in the genome or transcriptome. Once you have candidates, confirm each primer sequence with this site’s BLAST. The Tm and GC settings above are the design targets, and the annealing temperature still has to be optimised at the bench.

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