Phosphate-Modified Oligonucleotides. The Synthesis, Stereochemistry and ECO Ri Endonuclease Substrate Ability of Decanucleotides d[GGGAATTCCC] Bearing Altered Internucleotide Phosphate Function Between A and A¹

Abstract

An interaction between Eco RI endonuclease and decadeoxyribo-nucleotide GGGAATTOOC is followed by means of oligonucleotide analogues bearing modified internucleotide phosphate functions bridging both adenosine residues. While an o-alkyl group at this phosphate, despite the “side” of DNA alkylation, completely prevents DNA from hydrolysis, a phosphorothioate function replacing phosphate at the position between A and A moieties controls the hydrolysis in terms of the absolute configuration at phosphorus. The fact, that the Rp-isomer of d[GGGA(S)ATTOOC] possessing sulphur atom directed “inward” DNA is hydrolyzed by Eco RI endonuclease may indicate, that the pro-S oxygen at this particular phosphate is involved in an interaction with magnesium ion, a necessary factor for executive action of this endonuclease.