The eukaryotic translation initiation factor eIF4E elevates steady-state m7G capping of coding and noncoding transcripts

Methyl-7-guanosine (m⁷G) "cap" addition on 5' ends of RNA impacts virtually all levels of processing. Titrating capping of transcripts impacts on protein-coding capacity and, for noncoding RNAs, biochemical activity. Capping is widely considered a constitutive housekeeping activity with the expectation that ∼100% of transcripts will be capped at steady state. We developed two methods to quantify capping: quantitative CapIP and an enzymatic method, CapQ. Strikingly, steady-state RNA capping ranged from ∼30 to 50%, much lower than anticipated. eIF4E, a cap-binding protein implicated in human malignancy, elevated capping to ∼60 to 100% for selected transcripts, many of which act in cancer. Indeed, capping is elevated in high-eIF4E primary human cancer specimens. Thus, capping is a significant regulatory step in RNA metabolism.