A novel synthesis and detection method for cap-associated adenosine modifications in mouse mRNA

Kruse, Susanne; Zhong, Silin; Bodi, Zsuzsanna; Button, James; Alcocer, Marcos J. C.; Hayes, Christopher J.; Fray, Rupert

An interaction of m 7 G capped transcripts with the nuclear cap-binding complex (CBC) is important for promoting correct splicing 14 and 3'end formation 15 . After export from the nucleus, translation of most mRNAs is initiated with the recognition of the m 7 G cap by eukaryotic translation initiation factor 4E (eIF4E) 16 . This cap binding step is usually rate-limiting for translation. The m 7 G cap also protects the message from 5' to 3' exonuclease digestion. Compared to the well characterised role of m 7 G, relatively little is known regarding the function of 2' ribose methylation on the following nucleotides. The presence of a cap1 structure may promote binding to ribosomes 17 and can increase translational efficiency in vitro 18, 19 . Many animal viruses encode their own cap1 methylases 20, 21 and this may also help them to limit host immune responses 22, 23 . Whilst viral cap1 methylases are common viral cap2 methylases and m 6 Am methylases have not been reported. However, m 6 Am and cap2 structures can be found in viral mRNAs in vivo, presumably as a result of the action of the host cell's enzymes 24 . The functional consequences for an mRNA of possessing m 6 Am in a cap1 or a cap2 structure are not known.