Cap-specific terminal N 6 -methylation of RNA by an RNA polymerase II–associated methyltransferase

A cap-specific m 6 A writer N 6 ,2′- O -dimethyladenosine (m 6 Am) is present at the transcription start nucleotide of capped mRNAs in vertebrates. Akichika et al. quantified the abundance of this modification in the transcriptome and identified the writer protein, cap-specific adenosine methyltransferase (CAPAM), needed for this modification. CAPAM contains a unique structure that recognizes cap-specific N 6 -methyladenosine (m 6 A) as the substrate. The protein interacts with RNA polymerase II, suggesting that the modification occurs cotranscriptionally. The m 6 Am promotes the translation of capped mRNAs in a eIF4E-independent fashion. Science , this issue p. eaav0080