No abstract

In-frame stop codons mark the termination of translation. However, post-termination ribosomes can reinitiate translation at downstream AUG codons. In mammals, reinitiation is most efficient when the termination codon is positioned close to the 5′-proximal initiation site and around 78 bases upstream of the reinitiation site. The phenomenon was studied mainly in the context of open reading frames (ORFs) found within the 5′-untranslated region, or polycicstronic viral mRNA. We hypothesized that reinitiation of translation following nonsense mutations within the main ORF of p53 can promote the expression of N-truncated p53 isoforms such as Δ40, Δ133 and Δ160p53. Here, we report that expression of all known N-truncated p53 isoforms by reinitiation is mechanistically feasible, including expression of the previously unidentified variant Δ66p53. Moreover, we found that significant reinitiation of translation can be promoted by nonsense mutations located even 126 codons downstream of the 5′-proximal initiation site, and observed when the reinitiation site is positioned between 6 and 243 bases downstream of the nonsense mutation. We also demonstrate that reinitiation can stabilise p53 mRNA transcripts with a premature termination codon, by allowing such transcripts to evade the nonsense mediated decay pathway. Our data suggest that the expression of N-truncated proteins from alleles carrying a premature termination codon is more prevalent than previously thought.

Bacteriophages (phages), viruses that infect bacteria, are considered to be highly host-specific. To add to the knowledge about the evolution and development of bacteriophage speciation toward its host, we conducted a 21-day experiment with the broad host-range bacteriophage Aquamicrobium phage P14. We incubated the phage, which was previously isolated and enriched with the Alphaproteobacteria Aquamicrobium H14, with the Betaproteobacteria Alcaligenaceae H5. During the experiment, we observed an increase in the phage’s predation efficacy towards Alcaligenaceae H5. Furthermore, genome analysis and the comparison of the bacteriophage’s whole genome indicated that rather than being scattered evenly along the genome, mutations occur in specific regions. In total, 67% of the mutations with a frequency higher than 30% were located in genes that encode tail proteins, which are essential for host recognition and attachment. As control, we incubated the phage with the Alphaproteobacteria Aquamicrobium H8. In both experiments, most of the mutations appeared in the gene encoding the tail fiber protein. However, mutations in the gene encoding the tail tubular protein B were only observed when the phage was incubated with Alcaligenaceae H5. This highlights the phage’s tail as a key player in its adaptation to different hosts. We conclude that mutations in the phage’s genome were mainly located in tail-related regions. Further investigation is needed to fully characterize the adaptation mechanisms of the Aquamicrobium phage P14.