CAPAM: The mRNA Cap Adenosine N6-Methyltransferase

Abstract

The mRNA cap is a structure that protects mRNA from degradation and recruits processing and translation factors. A new mRNA capping enzyme has been identified, PCIF1/CAPAM, which methylates adenosine when it is the first transcribed nucleotide. This discovery is crucial for understanding the function of cap adenosine methylation.

Keywords: CAPAM; Pcif1; gene expression; m6Am; mRNA cap; mRNA cap methyltransferase.

Figure 1

mRNA Capping Enzymes Recruited to RNA Polymerase II (Pol II) During Transcription. During the initial phase of transcription, TFIIH phosphorylates the Pol II C-terminal domain (CTD) on serine 5. The capping enzymes RNGTT, RNMT–RAM, CMTR1, and CAPAM are then recruited to the phosphorylated RNA Pol II. Next to each capping enzyme is a cap structure that they produce, with the specific component added marked in red. RNA is synthesised with a 5′ triphosphate. RNGTT is a triphosphatase and guanylyltransferase that adds the inverted guanosine cap to nascent RNA. The other enzymes, RNMT-RAM, CMTR1 and CAPAM, are methyltransferases. RNA is depicted as a purple strand.