This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: When the coronavirus SARS-CoV-2 turned our world upside down, mRNA vaccines against COVID-19 brought a breakthrough. Their success established modified mRNA as a powerful foundation for vaccines and opened the way for new mRNA-based technologies, with potential applications ranging from vaccines against other infectious diseases to cancer immunotherapy.
Researchers led by Marina Rodnina and Panagiotis Poulis from the Max Planck Institute for Multidisciplinary Sciences (Göttingen, Germany) have now uncovered an important aspect of how such modified mRNAs are translated into proteins. In their study published in Nature Communications, they show why ribosomes can occasionally shift into the wrong reading frame when translating modified mRNA and how these errors can be largely avoided through mRNA sequence design. Our cells make proteins by reading messenger RNA (mRNA) three "letters" at a time.
Each group of three "letters," called a codon, specifies an amino acid in the protein. mRNA vaccines use the same machinery: They deliver synthetic mRNA that instructs our cells to produce a viral protein, which is then recognized by the immune system and causes a protective immune response in the body. A key feature of current mRNA vaccines is that the natural mRNA building block uridine (U) is replaced with a modified version, N1-methylpseudouridine. This modification reduces unwanted immune activation and promotes efficient protein production.
However, it can also affect how the ribosome moves along the mRNA. At certain sequences, the ribosome can occasionally slip forward by one letter, shifting the way all subsequent codons are read and producing an unintended protein. The Max Planck researchers have now unraveled why and how this frameshifting happens and identified strategies to avoid it.
To uncover the mechanism, the researchers combined experiments in human cells with a fully reconstituted in vitro translation system, allowing them to pinpoint where and when the ribosome slips. Using single-molecule fluorescence microscopy, they could then follow individual ribosomes in real time and observe how transfer RNAs (tRNAs), which read codons and deliver the corresponding amino acids, move during frameshifting. That revealed the exact trigger: N1-methylpseudouridine destabilizes the tRNA's interaction with the mRNA on the ribosome, making it more likely to shift by one nucleotide into the wrong reading frame.
"Importantly, frameshifting occurs only at particular mRNA sequences—and these can be avoided," Poulis says. For example, the researchers identified UUU C as a slippery sequence when U is replaced by N1-methylpseudouridine. Changing the sequence without changing the encoded protein, for example from UUU C to UUC C, almost completely abolished frameshifting.
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