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: TcoG036202.mRNA1 (TcoG036202.mRNA1), 2,293 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 2,293 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 CAAGGCAGTTTCGAAACGCA 1661–1680 20 59.971 50.000 TTGAAAGGAGCCTCGGCAAT 1891–1910 20 59.962 50.000 250 0.067
2 GTTTGGCAGCAGCATTTCCA 2002–2021 20 59.966 50.000 AGTGGCCAATACTCCAGCAC 2165–2184 20 60.035 55.000 183 0.069
3 GTTTGGCAGCAGCATTTCCA 2002–2021 20 59.966 50.000 CTTCCCTGCTGTCACATCGT 2106–2125 20 60.037 55.000 124 0.071
4 ATTGCCGAGGCTCCTTTCAA 1891–1910 20 59.962 50.000 TGGAAATGCTGCTGCCAAAC 2002–2021 20 59.966 50.000 131 0.072
5 TGCTGGTGTGCATTGATCCT 1241–1260 20 59.961 50.000 TGCTCCACAACAGCTCTCTG 1375–1394 20 59.966 55.000 154 0.073
Primer map pair 1 (lowest penalty) · product 250 bp at template position 1,661–1,910 · the template track shows a 1,500 bp window of the 2,293 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 794–2,293 of 2,293Template1,500 bp windowproduct 250 bp · template 1,661–1,910product 250 bpleft primer, template 1,661–1,680right primer anneals here, template 1,891–1,9107941,1691,5441,9182,293Amplicon250 bpleft primer CAAGGCAGTTTCGAAACGCA · 5′→3′right primer TTGAAAGGAGCCTCGGCAAT · its reverse complement binds the template strandinterior 210 bp1,6611,7231,7861,8481,910
Left primer
CAAGGCAGTTTCGAAACGCA
template 1,661–1,680 · 20 bp · Tm 59.971 °C · GC 50.000 %
Right primer
TTGAAAGGAGCCTCGGCAAT
template 1,891–1,910 · 20 bp · Tm 59.962 °C · GC 50.000 %

Amplicon sequence (5′→3′ on the template strand, 250 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.

CAAGGCAGTTTCGAAACGCAGTTCTGGGTTCCAGCTCCTCAGACAACGAAAAGCCCAGCGGTAAAGGACGGAAGAAAGCTAACAAAGGGATTGGACCCAGTGTCATGGTGTCGCGTGTTGATGTCGAGGAGGCGCTGGTGGACTTACAGCTCAGGCAGCCAAACTGCCGAGTGCGCATGTGTGAAACGGAGGAAGAATTTACCGAGCTGCTGACCATGTTCACTAAAGCTATTGCCGAGGCTCCTTTCAA

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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