Nascent chain interactions of proximal ribosomes drive homo-oligomer assembly

Accurate assembly of newly- synthesized proteins into functional oligomers is crucial for cell activity. In this study, we investigated whether direct interaction of two nascent proteins, emerging from nearby ribosomes (co-co assembly), constitutes a general mechanism for oligomer formation. We used a proteome-wide screen to detect nascent chain-connected ribosome pairs and identified hundreds of homomer subunits that co-co assemble in human cells. Interactions are mediated by five major domain classes, among which N-terminal coiled coils are the most prevalent. We were able to reconstitute co-co assembly of nuclear lamin in Escherichia coli, demonstrating that dimer formation is independent of dedicated assembly machineries. Co-co assembly may thus represent an efficient way to limit protein aggregation risks posed by diffusion-driven assembly routes and ensure isoform-specific homomer formation. Overall design: Screen of nascent chain dimerization in two human cell lines (HEK293-T and U2OS, 2 replicates each). Total translatomes from HEK293-T cells are also provided in 2 replicates. Similar screen performed with treatment of HEK293-T cell lysates with puromycin (2 replicates) or a titration of Proteinase K (4 conditions, 1 replicate). Similar screen performed in E.coli over-expressing a human gene candidate (5 genes tested, 4 of which are performed in 2 replicates).