Homomers are pervasive protein complexes in most proteomes that involved in all major cellular functions. The three steps in homomer formation are: translation by the ribosome, folding, and assembly into a protein complex. We hypothesize that the relative rates of these three steps are crucial to avoid misassembly in the context of the high nascent chain concentration of the polysome, i.e., the super-complex of multiple translating ribosomes from same mRNA molecule. To examine this, we tested a library of constructs that differ, among other properties, in the N- versus C-terminal position of the assembly (oligomerization) domain. By analyzing the misassembly rates of these constructs in vivo, in vitro and in silico, and by computationally analyzing thousands of native homomers, we show a set of spatiotemporal constraints that act to preserve the integrity of homomers. In conclusion, our results suggest that there has been significant selection in evolution to maintain a balance between translation and assembly.
