Abstract: New RNA cap analogs are disclosed containing one or more phosphorothioates groups. The analogs also contain modifications at the 2?-O position of 7-methylguanosine that prevent them from being incorporated in the reverse orientation during in vitro synthesis of mRNA and that hence are “anti-reverse cap analogs” (ARCAs). The ARCA modification ensures that the S atom is precisely positioned within the active sites of cap-binding proteins in both the translational and decapping machinery. The new S-ARCA analogs are resistant to in vivo decapping enzymes. Some S-ARCAs have a higher affinity for eIF4E than the corresponding analogs not containing a phosphorothioate group. When mRNAs containing the various S-ARCAs are introduced into cultured cells, some are translated as much as five-fold more efficiently than mRNAs synthesized with the conventional analog m7GpppG.

Abstract: The ability to synthesize capped RNA transcripts in vitro has been of considerable value in a variety of applications. However, one-third to one-half of the caps have, until now, been incorporated in the reverse orientation. Such reverse caps impair the translation of in vitro-synthesized mRNAs. Novel cap analogues, such as P1-3?-deoxy-7-methylguanosine-5?P3-guanosine-5?triphosphate and P1-3?-O,7-dimethylguanosine-5?P3-guanosine-5?triphosphate, have been designed that are incapable of being incorporated into RNA in the reverse orientation. Transcripts produced with SP6 polymerase using “anti-reverse” cap analogues were of the predicted length. Analysis of the transcripts indicated that reverse caps were not formed. The in vitro translational efficiency of transcripts with the novel “anti-reverse” cap analogues was significantly higher than that of transcripts formed with conventional caps.