Sequence-specific cleavage of RNA by Type II restriction enzymes

The ability of 223 Type II restriction endonucle-ases to hydrolyze RNA–DNA heteroduplex oligo-nucleotide substrates was assessed. Despite the significant topological and sequence asymmetry introduced when one strand of a DNA duplex is substituted by RNA we find that six restriction enzymes (AvaII, AvrII, BanI, HaeIII, HinfI and TaqI), exclusively of the Type IIP class that recognize palindromic or interrupted-palindromic DNA se-quences, catalyze robust and specific cleavage of both RNA and DNA strands of such a substrate. Time-course analyses indicate that some endo-nucleases hydrolyze phosphodiester bonds in both strands simultaneously whereas others appear to catalyze sequential reactions in which either the DNA or RNA product accumulates more rapidly. Such strand-specific variation in cleavage suscepti-bility is both significant (up to orders of magnitude difference) and somewhat sequence dependent, notably in relation to the presence or absence of uracil residues in the RNA strand. Hybridization to DNA oligonucleotides that contain endonuclease recognition sites can be used to achieve targeted hydrolysis of extended RNA substrates produced by in vitro transcription. The ability to ‘restrict ’ an RNA–DNA hybrid, albeit with a limited number of restriction endonucleases, provides a method whereby individual RNA molecules can be targeted for site-specific cleavage in vitro