The Chemical Entities of Biological Interest (ChEBI) ontology is downloaded weekly from EMBL-EBI at http://www.ebi.ac.uk/chebi/. The data is made available under the Creative Commons License (CC BY 3.0, http://creativecommons.org/licenses/by/3.0/). For more information see: Degtyarenko et al. (2008) ChEBI: a database and ontology for chemical entities of biological interest. Nucleic Acids Res. 36, D344–D350.
An oligonucleotide in which one of the non-bridging oxygens in each phosphodiester linkage has been replaced by sulfur. The main application of phosphorothioate linkages in an oligonucleotide is to protect the oligonucleotide from nuclease degradation.