mRNA Pseudouridylation Effects on Coding

It has long been known that pseudouridine (Ψ) is an abundant post-transcriptionally modified nucleotide having chemical properties distinct from those of all other naturally occurring nucleotides. It is thus conceivable that Ψ, once introduced into mRNA codons, may uniquely contribute to codon-anticodon recognition, thereby impacting the final polypeptide product. Yet, until recently, the study of mRNA pseudouridylation has been hampered by a lack of sensitive modification assays and effective experimental systems. In the past several years, however, our lab and others have made substantial progress towards developing convenient yet sensitive modification assays and experimental systems that have made it possible to carry out detailed studies of mRNA pseudouridylation and its effect on coding. In fact, we have already made some remarkable observations.

In particular, our preliminary results indicate that mRNAs almost certainly contain naturally occurring Ψs. Our results also show that Ψ, when introduced into triplet-nucleotide codons (including three nonsense codons and one sense codon tested), changes their coding specificities. While remarkable, our findings also raise at least three important questions. First, how widespread is Ψ in mRNA? Second, would substitution of Ψ in place of a natural uridine (U) in a sense codon change its coding specificity, and if so, what amino acid would the pseudouridylated codon code for? Third, how are pseudouridylated codons recognized in the context of the global ribosomal machinery? Having generated remarkable preliminary results, we are now in an excellent position to carry out experiments to address these questions.

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