A ribosome exit tunnel component is required for robust expression of the Drosophila hox gene, abdominal A

Ribosomes, the molecular machines responsible for protein synthesis, are fundamental to all cellular life. Although the higher-level architecture of ribosomes is conserved, a small subunit acting as the mRNA decoding site and a large subunit that catalyses peptide bond formation, there are differences in the numbers of components of each of the subunits between the 3 domains of life. Despite their well-established role in translating genetic information into functional proteins, many complexities in ribosome biology and functionality are only just being revealed. Defects in ribosomal components contribute to a class of disorders termed ribosomopathies that come with a range of symptoms and severities. Here we show that a mutation in the Drosophila ribosomal protein RpL39 causes an anterior-posterior embryonic patterning defect through impaired accumulation of the hox protein Abdominal-A (abdA). Deletions uncovering subunits of the Nascent peptide-Associated Complex (NAC) and Ribosome-Associated Complex (RAC) act as genetic enhancers of the RpL39 mutation leading us to speculate that RpL39 forms a relay between the nascent peptide in the exit tunnel and the exterior surface of the ribosome, modulating the interaction with these ribosomally-associated complexes. This work enhances our knowledge of the roles played by individual ribosome components and feeds into our understanding of the mechanisms of ribosome quality control.