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A Python3 package for melting temperature calculation of oligonucleotides hybridization and secondary structures.

Project description



A Python3 package for melting temperature calculation of oligonucleotides hybridization and secondary structures.


  • Handles DNA:DNA, RNA:RNA and DNA/RNA hybridizations.
  • Corrects for both salt and chemicals.
  • Compatible with UNAfold (OligoArrayAux) output for direct salt and chemicals (denaturants) correction.
  • Produces melting curves for the provided sequence.
  • Input either as single sequence or FASTA file.
  • Slightly faster than BioPython.SeqUtils.MeltingTemp.
  • Provides dG, dS and dH alongside melting temperature.


  • Does not handle mismatches or dangling ends
  • Does not handle ambiguous bases


To install, run the following:

git clone
cd oligo-melting
sudo -H pip3 install .

To uninstall run the following from within the repository folder:

sudo -H pip3 uninstall oligo_melting

To update, first uninstall, and then run the following from within the repository folder.

git pull
sudo -H pip3 uninstall oligo_melting
sudo -H pip3 install .


From command line


The melt_duplex command allows to calculate the melting temperature of a nucleic acid duplex, provided the sequence of one of the two strands.

The hybridization delta free energy calculation is based on the N-N thermodynamic values in literature and is available for DNA:DNA[3], RNA:RNA[1] and DNA:RNA[2] duplexes. The melting temperature calculation is based on Santalucia, 1998[4]. Sodium and cagnesium concentration correction is based on the work of Owczarzy et al[5][6]. Formamide correction can be performed based on two different published models[7][8].

  • Use the -t option to specify the type of nucleic acid duplex.
  • Use --fa-mode to switch between linear melting temperature formamide-based correction[7] and linear ΔG formamide-based correction[8].
  • Use --fa-mvalue together with --fa-mode wright to specify the m-value for the formamide-based correction.
  • Provide the path to a fasta file instead of a single sequence to calculate the melting temperature of every sequence in the file.
  • Use the -v option to trigger the verbose mode, which provides more details for every single sequence.
  • Use -C for the temperature in degree Celsius instead of Kelvin.
  • Use --out-curve to specify a file where to save estimated single-sequence melting curves with temperature range and step around the melting temperature as defined with --t-curve.

Secondary structure

The melt_secstr script allows to correct the melting temperature of a nucleic acid secondary structure, previously calculated with OligoArrayAux, and to produce the corresponding melting curves.

As a library

Import the package and use the corresponding functions.

import oligo_melting as OligoMelt


# Calculate melting temperature for 25uM oligos
(name, g, h, s, tm, seq) = OligoMelt.Duplex.calc_tm(seq, oligo_conc = 25e-6)

# Adjust for 300 mM [Na+]
tm = OligoMelt.Duplex.adj_ions(tm, 0.3, 0, seq)

The Duplex module contains functions for duplex hybridization and melting temperature calculation, while the SecStr module contains similar methods for evaluating secundary structure melting temperatures.


  • [1]: Freier et al, PNAS(83), 1986;
  • [2]: Sugimoto et al, Biochemistry(34), 1995.
  • [3]: Allawi & Santalucia, Biochemistry(36), 1997;
  • [4]: SantaLucia, PNAS(95), 1998;
  • [5]: Owczarzy et al, Biochemistry(43), 2004;
  • [6]: Owczarzy et al, Biochemistry(47), 2008;
  • [7]: McConaughy et al, Biochemistry(8), 1969;
  • [8]: Wright et al, Appl. env. microbiol.(80), 2014.


MIT License
Copyright (c) 2017 Gabriele Girelli

This project comes from the potpourri sandbox. \( ゚ヮ゚)/

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