Creating RNA bulges: cleavage of RNA in RNA/DNA duplexes by metal ion catalysis.

The manipulation of a single-stranded RNA target by forming different RNA/antisense hybrids demonstrates the possibility of cleaving the RNA strand within duplexes. This was achieved using the sequence composition of the antisense oligonucleotide, an approach that results in various bulges [unpaired base(s)] in the RNA target, which is then cleavable at these specific bulge sites under free metal ion or metal complex catalysis. RNA cleavages promoted by metal ions were performed under mild conditions and characterized by separating the RNA fragments carrying end label. The observed products result from intramolecular transesterification causing RNA strand scission. No detectable cleavage of the RNA was observed with either a fully complementary RNA/antisense hybrid or a bulged base in the antisense strand. A molecular modeling study of the RNA backbone suggests that the local conformation of the RNA backbone at a bulge in such hybrid duplexes greatly facilitates the metal-assisted catalytic cleavage. Endonucleolytic RNA cleavage within an RNA/antisense hybrid by metal complexes attached to the antisense oligonucleotide might lead to a new approach in antisense technology with artificial ribonucleases which operate with catalytic turnover.