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: scaffold21.g153.t1 (scaffold21.g153.t1), 2,120 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 2,120 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 CTTGAAGAACTCGATGCGCG 183–202 20 59.976 55.000 TCTCCGGTCCGTCAAGTACT 320–339 20 59.963 55.000 157 0.062
2 CGCTTGAAGAACTCGATGCG 181–200 20 59.976 55.000 TCTCCGGTCCGTCAAGTACT 320–339 20 59.963 55.000 159 0.062
3 TGATGGCGAAGGTCGAACAA 1601–1620 20 59.966 50.000 AGCCCACTGCCATAACACTC 1740–1759 20 60.035 55.000 159 0.069
4 CTGCGGGGAGGACAAATTCT 1329–1348 20 60.035 55.000 TTGTTCGACCTTCGCCATCA 1601–1620 20 59.966 50.000 292 0.069
5 GTTACTGCGGGGAGGACAAA 1325–1344 20 59.964 55.000 TTGTTCGACCTTCGCCATCA 1601–1620 20 59.966 50.000 296 0.070
Primer map pair 1 (lowest penalty) · product 157 bp at template position 183–339 · the template track shows a 1,500 bp window of the 2,120 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 2,120Template1,500 bp windowproduct 157 bp · template 183–339product 157 bpleft primer, template 183–202right primer anneals here, template 320–33913767511,1251,500Amplicon157 bpleft primer CTTGAAGAACTCGATGCGCG · 5′→3′right primer TCTCCGGTCCGTCAAGTACT · its reverse complement binds the template strandCTTGAAGAACTCGATGCGCGTCTCCGGTCCGTCAAGTACTinterior 117 bp183222261300339
Left primer
CTTGAAGAACTCGATGCGCG
template 183–202 · 20 bp · Tm 59.976 °C · GC 55.000 %
Right primer
TCTCCGGTCCGTCAAGTACT
template 320–339 · 20 bp · Tm 59.963 °C · GC 55.000 %

Amplicon sequence (5′→3′ on the template strand, 157 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.

CTTGAAGAACTCGATGCGCGAATACGGGGACACGATGCGATGCTCAAAAACAATTATATGCGAATAAACATGCTGGAAAACACGGAGAGAAAAAACAGCAAAATGGATGAAATGATAGACAAGGGAATGTTTCACAAAGTACTTGACGGACCGGAGA

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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