Leslie, J. M. | bioRxiv Science

bioRxiv2026

Glutamine codon-driven translational readthrough reveals context-dependent stop codon decoding fidelity

Deviations from the canonical genetic code include reassignment of UAA/UAG stop codons to glutamine in divergent eukaryotes, and tRNAGln has been shown to mediate near-cognate stop codon readthrough in canonical-code organisms. However, the sequence determinants and mechanistic basis of this decoding event remain poorly understood. Using ribosome profiling, quantitative immunoblotting, and mass spectrometry in Saccharomyces cerevisiae, we demonstrate that premature stop codon readthrough efficiency is governed by both local glutamine codon context and the global glutamine codon content of the mRNA. A QXQ motif flanking the stop codon promotes baseline readthrough, which is amplified in proportion to total transcript glutamine codon abundance. Mass spectrometry confirms that glutamine is specifically inserted at the premature stop, with no flanking miscoding, implicating tRNAGln competition with the release factor as the mechanistic basis of readthrough. Consistent with this model, yeast proteins terminating in short C-terminal glutamine repeats are evolutionarily enriched for strong stop codon contexts, suggesting selective pressure to reinforce termination fidelity at readthrough-prone loci.

molecular biology↗

bioRxiv2021

Programmed ER fragmentation drives selective ER inheritance and degradation in budding yeast meiosis

The endoplasmic reticulum (ER) is a membrane-bound organelle with diverse, essential functions that rely on the maintenance of membrane shape and distribution within cells. ER structure and function are remodeled in response to changes in cellular demand, such as the presence of external stressors or the onset of cell differentiation, but mechanisms controlling ER remodeling during cell differentiation are not well understood. Here, we describe a series of developmentally regulated changes in ER morphology and composition during budding yeast meiosis, a conserved differentiation program that gives rise to gametes. During meiosis, the cortical ER undergoes fragmentation before collapsing away from the plasma membrane at anaphase II. This programmed collapse depends on the meiotic transcription factor Ndt80, conserved ER membrane structuring proteins Lnp1 and reticulons, and the actin cytoskeleton. A subset of ER is retained at the mother cell plasma membrane and excluded from gamete cells via the action of ER-plasma membrane tethering proteins. ER remodeling is coupled to ER degradation by selective autophagy, which is regulated by the developmentally timed expression of the autophagy receptor Atg40. Autophagy relies on ER collapse, as artificially targeting ER proteins to the cortically retained ER pool prevents their degradation. Thus, developmentally programmed changes in ER morphology determine the selective degradation or inheritance of ER subdomains by gametes.

cell biology↗