The formation of triple stranded helix of oligodeoxyribonucleotides containing 8-oxo-2 '-deoxyadanosine

Triple stranded DNA helix (triplex) formation is limited by pH and the sequ ence of oligodeoxyribonucleotide. In this study, the 8-oxo-2'-deoxyadenosin e (8-oxoA) can replace 2'-deoxycytidine for forming a base triad with a bas e pair guanine and cytosine. The target for the tripler formation is a moti f of a promotor (5'-d-TTGGGGGGGAA, -3 - -12 of PKCalpha m-RNA) of mouse pro tein kinase C-alpha. The probes contain 20 bases with a common sequence 5'- d-XXXXXXTTCCCCCCAA. The XXXXXX portion may contain either 5-methyl-2'-deoxy cytidines, six 8-oxoA's or both. Only the probe with a motif of six 8-oxoA' s can for triplex with the target in the presence of magnesium ion and sper mine at neutral pH. Therefore, 8-oxoA is useful for tripler formation under physiological conditions.