The phosphorothioate (PS) bond substitutes a sulfur atom for a non-bridging oxygen in the phosphate backbone of an oligo. This modification renders the internucleotide linkage resistant to nuclease degradation. Phosphorothioate bonds can be introduced between the last 3-5 nucleotides at the 5'- or 3'-end of the oligo to inhibit exonuclease degradation. Including phosphorothioate bonds throughout the entire oligo will help reduce attack by endonucleases as well.
Phosphorothioate Bond Entry
Bond Name
Symbol
Example
Phosphorothioated DNA bases
_*
e.g. A*
Phosphorothioated RNA bases
r_*
e.g. rA*
Phosphorothioated 2' O-methyl bases
m_*
e.g. mA*
Phosphorothioated Affinity Plus (locked nucleic acid) bases