We do not know the exact set of mechanisms causing this, or any other transcription-phase modification (or post-transcription mods, for that matter). I say the mechanism likely involves operations performed by trans or _preexisting_ ribosomal-protein complexes. Regardless, Cheung and colleagues performed masterfully.\n\nThe central dogma states that cellular genetic information flows exclusively from DNA to RNA to proteins. Cheung et al. show that RNA modification information can come from some place else.\n\nKeep in mind that DNA isn't "smart." DNA is but a substrate of molecular information harvested and transformed by the cell's molecular networks in often custom ways suited to the local part of the cell's microenvironment.\n\nThe problem with the glib central dogma is that it answers a question that is wrong headed. That is, the central dogma assumes that the cell is a centrally controlled machine. It is not. In fact, modifications occur generally, universally. Therefore, the central dogma is irrelevant and has always been so. Get real, folks.