A sequence of the rabbit α-globin mRNA is the primary target for ODN1, an unmodified 15-nucleotide (nt) antisense oligodeoxyribonucleotide (oligo). ODN1 prevented in vitro translation of both α- and β-globin mRNAs in wheat germ extract. Nine secondary sites exhibiting more than 60% complementarity with ODN1 were present m the β-globin message. The ODN1 inhibition of β-globin synthesis was shown to be mediated by RNase H cleavage of the β-globin mRNA at three partially complementary sites. Sandwich-type oligos consisting of a stretch of unmodified nt with a few methylphosphonate residues at both 5′ and 3′ ends were derived from ODN1. We have demonstrated that one such analogue ( ODN2), with five phosphodiester linkages in the central region, exhibited improved specificity for α-globin mRNA compared with the unmodified parent 15-mer, due to a reduced ability of RNase H to cleave β-mRNA/ ODA2 mismatched duplexes.
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