Figure 1.

Overview of chemical capping. (A) Representative example of a 5′-monophosphate RNA capped through reaction with a guanosine 5′-phosphoroimidazolide forming a 5′-5′ phosphodiester linkage. (B) Structure of 41 distinct capped 25mer RNAs varying the nucleotide cap (guanosine, adenosine, cytidine, thymidine or inosine) and the length of the polyphosphate bridge (di-, tri- or tetraphosphate).