Complete Chemical Synthesis of Minimal Messenger RNA by Efficient Chemical Capping Reaction.

Site-specific chemical modification of mRNA can improve its translational efficiency and stability. For this purpose, it is desirable to develop a complete chemical synthesis method for chemically modified mRNA. The key is a chemical reaction that introduces a cap structure into the chemically synthesized RNA. In this study, we developed a fast and quantitative chemical capping reaction between 5'-phosphorylated RNA and N7-methylated GDP imidazolide in the presence of 1-methylimidazole in the organic solvent dimethyl sulfoxide. It enabled quantitative preparation of capping RNA within 3 h. We prepared chemically modified 107-nucleotide mRNAs, including N6-methyladenosine, insertion of non-nucleotide linkers, and 2'-O-methylated nucleotides at the 5' end and evaluated their effects on translational activity in cultured HeLa cells. The results showed that mRNAs with non-nucleotide linkers in the untranslated regions were sufficiently tolerant to translation and that mRNAs with the Cap_2 structure had higher translational activity than those with the Cap_0 structure.

N6-methyl adenosine in siRNA evades immune response without reducing RNAi activity.

siRNA is a powerful method to suppress specific gene expression and has recently been utilized for molecular biology as well as medicine. However, introduction of dsRNA stimulates immune-responses as side-effects. In the present study, we utilized N6-methyl adenosine, one of the natural modified nucleosides, instead of adenosine in siRNA. When adenosine in the passenger or guide strand of siRNA was completely replaced with N6-methyl adenosine, the immune response against siRNA was evaded without any reduction in RNAi activity. This knowledge will promote the medical application of siRNA and enhance our understanding on cellular discrimination of non-self and self dsRNA.