Synthesis of Site-Specifically Modified Long-mer RNAs

Site-specific functionalization of RNA and DNA molecules has become a major task in nucleic acid chemistry. Synthetic RNAs are required for a large number of applications. Beyond synthetic RNA for antisense, aptamer, ribozyme, and siRNA technologies, oligoribonucleotides carrying site-specific modifications for structure and function studies are needed. A wide variety of monomer-building blocks is commercially available to be used for site-specific incorporation by solid-phase RNA synthesis. However, the efficient chemical preparation of RNA is limited to oligomers of about 60–70 nucleotides. Therefore, efficient strategies for fragment ligation or other alternative novel protocols are required. We here provide an overview on our work on the synthesis of site-specifically modified long-mer RNAs, focusing on enzymatic and chemical ligation of synthetic RNA fragments and on ribozyme-mediated sequence exchanges.