Ligation of oligonucleotides to nucleic acids or proteins via disulfide bonds

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Abstract
We have developed general methods for joining together, via cleavable disulfide bonds, either two unprotected polynucleotides or a polynucleotide and a peptide or protein. To join two oligonucleotides, each is first converted to an adduct in which cystamine is joined to the 5''-terminal phosphate of the oligonucleotide by a phosphoramidate bond. The adducts are mixed and reduced with dithiothreitol. The dithiothreitol is then removed by dialysis. Oxidation by atmospheric oxygen occurs to yield the required dimer. To join an oligonucleotide to a cysteine-containing peptide or protein, the 5''-cystamine oligomer is first converted to a 2''-pyridyldisulfide adduct and then reacted with an excess of the peptide or protein. If the peptide does not contain a free cysteine residue, it is first treated with iminothiolane to introduce one or more sulfhydryl groups. We have used these procedures to join a 16 mer deoxynucleotide probe and MDV-1 RNA, a substrate of QB RNA polymerase. This adduct hybridizes with a complementary target DNA. We have also joined a 16mer probe to peroxidase and MDV-1 RNA to human IgG. The probe-peroxidase adduct maintains enzymatic activity and the MDV-1 RNA-IgG adduct binds to a complementary anti-IgG.