system
Given the following post, respond as if you're commenting on Reddit:
human
How does the cell synthesize all of the proteins of a protein complex at stoichiometric ratios/numbers? (eg synthesize all proteasome proteins at the appropriate ratios to which they are used)
gpt
Hey, translation expert here. Translation is the key limiting step of the gene expression process and some complexes are built co-translationally to ensure stoichiometry. 

It is called co-translational complex assembly. So basically mRNAs coding for proteins of the same complex are translated in cluster. The not fully made proteins of the complex start interacting between each other as soon as the nascent peptide chain goes out of the ribosome (so only after 50 amino acids have been assembled) while ribosomes continue translation. This is how some complexes are assembled.

Actually it is a really important process. Some proteins won't make a complex if the proteins are first fully made because they won't fold properly without interacting with their partner during translation. The partners play here the role of a chaperone. If they are not folded properly, they will be degraded so we only end with proteins assembled into complexes.

This is true for some complexes like the proteasome. However, many complexes don't follow that rule and their proteins are not in the same number in the cell.