Fukuchi, S. | Search bioRxiv

bioRxiv2026

Neuronal stop-codon readthrough is associated with ribosome pausing and alters protein localization in Drosophila

Stop-codon readthrough (RT) diversifies proteomes and is particularly prominent in neurons, suggesting its importance in nervous systems. However, the regulatory logic that specifies neuronal RT and the structural and cellular consequences of the resulting C-terminal protein extensions remain poorly understood. Here we leverage neuron-specific ribosome profiling datasets in Drosophila to construct an in vivo atlas of 163 neuronal RT transcripts. Sequence- based modeling distinguished RT from non-RT transcripts and highlighted an extended post-stop region enriched for stable predicted RNA structures. Beyond these cis-associated features, ribosome-footprint analysis revealed pronounced stop-codon pausing on RT transcripts, accompanied by upstream periodic peaks from the stop codon consistent with ribosome queuing. At the protein level, neuronal RT appended polypeptides enriched with polar residues and intrinsically disordered regions (IDRs). Finally, an in vivo dual-color reporter showed that RT of the RNA-binding protein Bru3 alters localization from the nucleus to cytoplasmic granules. Together, our results suggest that neuronal RT is associated with structured post-stop RNA regions that reshape termination dynamics and can produce IDR-rich C-terminal protein extensions with distinct subcellular localization.

molecular biology↗

bioRxiv2024

Longer Internal Exons Tend to Have More Tandem Repeats and Experience Insertions and Deletions More Frequently

Insertions and deletions (indels) in eukaryotic proteins are known to preferentially encode intrinsically disordered regions (IDRs), protein regions that by themselves do not form unique three-dimensional structures. As a previous investigation showed that long internal exons tend to encode IDRs in eukaryotes in general, we thought it worthwhile to analyze how indels alter internal exons and affect IDRs of the encoded proteins. For consideration of evolutionary roles indels play, we decided to select indels commonly observed in all variants ("fixed" indels) since indels in minor variants may represent transient aberrations in splicing. Here, by comparison of orthologous variants of closely related species together with those of outgroups, we identified fixed indels in the internal exons in four mammals and two flies. The fixed indels are nearly always nonframeshifting, short, and mostly encode IDRs. On average 51% of inserted and 40% of deleted residues are attributable to alterations in tandem repeats. Deletion tends to occur more frequently than insertion does and indels are generally more prevalent in long internal exons. Tandem repeats occur preferentially in long internal exons, indicating that their alterations account for the high frequency of indels in long internal exons. Also, since tandem repeats mostly encode IDRs, this finding at least partially explains the high incidence of IDRs in long internal exons. We propose that long internal exons had been produced in early eukaryotes mainly by repeat expansion that added IDRs to the encoded proteins but are experiencing frequent indels by alterations in tandem repeats.

bioinformatics↗