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: g1957.t1 (g1957.t1), 3,057 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 3,057 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 CCAAGAACGCCAACAGGTTG 876–895 20 59.969 55.000 ACCTCCCTTGCATTCAGCTC 1123–1142 20 60.035 55.000 267 0.065
2 CCAAGAACGCCAACAGGTTG 876–895 20 59.969 55.000 CCTCCCTTGCATTCAGCTCA 1122–1141 20 60.035 55.000 266 0.065
3 ACCCCATGAAAGGATGGCTG 2553–2572 20 60.033 55.000 GACGTCTTCTGCCAACAGGA 2714–2733 20 59.966 55.000 181 0.066
4 ACCCCATGAAAGGATGGCTG 2553–2572 20 60.033 55.000 CGTCTTCTGCCAACAGGACT 2712–2731 20 59.966 55.000 179 0.067
5 CCAAGAACGCCAACAGGTTG 876–895 20 59.969 55.000 GGTTGATCACCTCCCTTGCA 1131–1150 20 59.962 55.000 275 0.069
Primer map pair 1 (lowest penalty) · product 267 bp at template position 876–1,142 · the template track shows a 1,500 bp window of the 3,057 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 259–1,758 of 3,057Template1,500 bp windowproduct 267 bp · template 876–1,142product 267 bpleft primer, template 876–895right primer anneals here, template 1,123–1,1422596341,0091,3831,758Amplicon267 bpleft primer CCAAGAACGCCAACAGGTTG · 5′→3′right primer ACCTCCCTTGCATTCAGCTC · its reverse complement binds the template strandinterior 227 bp8769431,0091,0761,142
Left primer
CCAAGAACGCCAACAGGTTG
template 876–895 · 20 bp · Tm 59.969 °C · GC 55.000 %
Right primer
ACCTCCCTTGCATTCAGCTC
template 1,123–1,142 · 20 bp · Tm 60.035 °C · GC 55.000 %

Amplicon sequence (5′→3′ on the template strand, 267 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.

CCAAGAACGCCAACAGGTTGAGAGCATTGTAAGGTTGCTGACACACAGATACAATCAGCTGTTGGACATGTGGGAAAAACGATGGAAAGAACTGATGCAGTGCATGGACCTACGGGATTTTGAAGCTGGGTATAAGAAGGTGATCGATTGGGTTCTTGGGCCAGGAGAGCGTTATTTATCAACATCAAAAGATATTGGAGATTCAGTAATCAGCTGTGAAATTTTAAGAAAAGAACACGAAGAATTTGAGCTGAATGCAAGGGAGGT

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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