Selenium modification of nucleic acids: preparation of phosphoroselenoate derivatives for crystallographic phasing of nucleic acid structures

This protocol describes a simplified means of introducing an anomalously scattering atom into oligonucleotides by conventional solid-phase synthesis. Replacement of a nonbridging phosphate oxygen in the backbone with selenium is practically suitable for any nucleic acid. The resulting oligonucleotide P-diastereomers can be separated using anion exchange HPLC to yield diastereomerically pure phosphoroselenoates (PSes). The total time for the synthesis and ion-exchange HPLC separation of pure PSe is approximately 60 h.