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 coupled to structured post-stop RNA regions that reshape termination dynamics and can produce IDR-rich C-terminal protein extensions with distinct subcellular localization.