Published on Aug. 18, 2020 in Cell Rep volume 32 (7).
PubMed ID: 32814042
DOI: 10.1016/j.celrep.2020.108038
Abstract:
The 5' end of eukaryotic mRNAs is protected by the m<sup>7</sup>G-cap structure. The transcription start site nucleotide is ribose methylated (Nm) in many eukaryotes, whereas an adenosine at this position is further methylated at the N<sup>6</sup> position (m<sup>6</sup>A) by the mammalian Phosphorylated C-terminal domain (CTD)-interacting Factor 1 (PCIF1) to generate m<sup>6</sup>Am. Here, we show that although the loss of cap-specific m<sup>6</sup>Am in mice does not affect viability or fertility, the Pcif1 mutants display reduced body weight. Transcriptome analyses of mutant mouse tissues support a role for the cap-specific m<sup>6</sup>Am modification in stabilizing transcripts. In contrast, the Drosophila Pcif1 is catalytically dead, but like its mammalian counterpart, it retains the ability to associate with the Ser5-phosphorylated CTD of RNA polymerase II (RNA Pol II). Finally, we show that the Trypanosoma Pcif1 is an m<sup>6</sup>Am methylase that contributes to the N<sup>6</sup>,N<sup>6</sup>,2'-O-trimethyladenosine (m<sup>6</sup><sub>2</sub>Am) in the hypermethylated cap4 structure of trypanosomatids. Thus, PCIF1 has evolved to function in catalytic and non-catalytic roles.