Practice question

Five prime capping of messenger RNA occurs predominantly in nucleus, co-transcriptionally while polymerase II remains bound to DNA template. Capping enzymes RNA triphosphatase, guanylyltransferase, and methyltransferase are recruited to promoter-proximal polymerase via binding to Serine five phosphorylated C-terminal domain. Enzymatic addition of 7-methylguanosine via five prime to five prime triphosphate linkage happens within first minutes of transcription when nascent RNA emerges. Resulting cap binding complex CBP20 and CBP80 protects transcript from nuclear exonucleases, facilitates splicing of first intron, and directs export through nuclear pore mediated by NXF1 pathway.