Behind the scene:1. Code for Degenerate Oligos
A A C C G G T T U T M (AC) R (AG) W (AT) S (CG) Y (CT) K (GT) V (ACG) H (ACT) D (AGT) B (CGT) N (ACGT)Any other letters will be ignored, so you can paste in a nucleotide sequences with spaces and numbers.
2. Melting temperature and annealing temperature Melting temperature is the temperature at which 50% of the oligo and its perfect complement are in duplex. PCR annealing temperature a few degree (4-6) lower than the melting temperature is usually used to increase the probability of primer binding. There are two options for calculating the melting temperature. The first uses the simple rule of 2 degree for each A or T and 4 degree for each C or G.
Melting temperature = 4 * Number of G or C + 2 * Number of A or T.
The second "Nearest N" predicts melting temperature using the "Nearest Neighbor" model (Jhon SantaLucia, Proc. Natl. Acad. Sci. Vol. 95, p1460-1465 (1998)). The cation concentration is assumed to be 50 mM and the primer concentration is assumed to be 200 nanomolar. The "Nearest N" is presented because it is more accurate and other formulae can be viewed as approximations of the "Nearest N".
The "Nearest N" formula has a correction for primer concentration. If lower or higher primer concentration is used, the rule-of-thumb is that for each two fold increase or decrease in the primer concentration, the melting temperature should increase or decrease by 1 degree. (Click here to see the relationship between primer concentration and melting temperature.)
For degenerate primers, the effective concentration is lower because of degeneracy. Users don't need to adjust for the lowered effective concentration if using the "Nearest N" formula, Primo has already taken that into account. Users are suggested to select the "Nearest N" formula if template sequences consist of degenerate codes.
To compare melting temperatures calculated using the two formulae, type or copy the primer sequence into the "2nd primer" field, and mouse-click on the text field. The melting temperature will be calculated using the selected formula. Click here to see the melting temperatures calculated using both formulae for some commonly used PCR and sequencing primers.
For degenerate nucleotides, an average is used.
3. Primer-primer dimer
P1: 5'-...GGCGATCG-3' |||||| 3'-GCTAGCGG...-5' : P1or
P1: 5'....AGGGCCC-3' || | 3'-CGCGAAT...-5' : P2The following single-base pair is also not allowed:
P1: 5'-...AGGTCGCG-3' | 3'-CGGATT...5' : P2
4. Methylated and un-methylated primers
Methylated primers recognize the converted sequence where CpG remain unchanged. Unmethylated primers pairs with the template where every cytosines have been converted to thymidine.
At least one CpG must be present in the MSP primer and CpG at the 3'-end of the primer is preferred.
Batch modeTo use the batch mode, select the batch mode checkbox and input multiple sequences in the following format:
>seq1 0-100 -100-0 catctccgagaggaaggcgaactcgaggagagcgatccggagcagcatggagtcctctgcagata gactagccagggccagcggccctgggccgtgagcacgaggtgcgggcactgctggaagccggggc ttcaccaaacgccccgaacactttcggtcgtaccccgatacaggt >seq2 GCTTGAGCCCAGGAGTTCGAGGCTGCAGTGAGCTGTGATCGCACCACTGCACTCCAGCTT GGGTGAAAGAGTGAGCCCCATCTCCAAAACGAACAAACAAAAAATCCCAAAAAACAAAAG AACTCAGCCAAGTGTAAAAGCCCTTTCTGATCCCAGGTCTTAGTGAGCCACCGGCGGGGC TGGGATTCGAACCCAGTGGAATCAGAACCGTGCAGGTCCCATAACCCACCTAGACCCTAG CAACTCCAGGCTAGAGGGTCACCGCGTCTATGCGAGGCCGGGTGGGCGGGCCGTCAGCTC
Each sequence starts with an info line with a > sign. The description of the sequence may be followed by the optional 5' and 3' range for forward or reverse primers. The three fields are separated by "tab."
If the range value starts with a minus sign, then the counting will be from the 3'-end of the sequence. If both ranges are missing in the info line, the input value from the Primo interface will be used. If only one range is present in the info line, that value will be used for designing forward or reverse primer only. It will be ignored for selecting pairs of forward and reverse primers.