Codon-specific ribosome stalling reshapes translational dynamics during branched-chain amino acid starvation
Background: Cells regulate protein synthesis in response to fluctuating nutrient availability through mechanisms that affect both translation initiation and elongation. Branched-chain amino acids, leucine, isoleucine, and valine, are essential nutrients. However, how their depletion affects translation remains largely unclear. Here, we investigate the immediate effects of single, double, and triple branched-chain amino acid deprivation on translational dynamics in NIH3T3 cells using RNA-seq and ribosome profiling. Results: All starvation conditions increased ribosome dwell times, with pronounced stalling at all valine codons during valine and triple starvation, whereas leucine and isoleucine starvation produced milder, codon-specific effects. Notably, stalling under isoleucine deprivation largely decreased under triple starvation. Positional enrichment of valine codons near the 5' end and downstream isoleucine codons potentially contributes to these patterns, suggesting a possible elongation bottleneck that influences translational responses under branched-chain amino acid starvation. The presence of multiple valine stalling sites was associated with decreased protein levels. Finally, codon-specific dwell time changes correlated strongly with patterns of tRNA isoacceptor charging. Conclusions: Together, these findings suggest that differential ribosome stalling under branched-chain amino acid starvation reflects a balance between amino acid supply, tRNA charging dynamics, codon position, and stress-response signaling. Overall design: NIH3T3 mouse fibroblast cells were grown either in complete medium (control) or in medium lacking specific branched-chain amino acids for 6 hours.