Figure 6.

Three different scenarios for the fine-tuning of protein complexes can potentially underlie the observed cell type-specific variations. For each scenario, the left panel shows the expected change in subunit expression after normalization for complex abundance. Red arrow indicates upregulation and blue arrow downregulation. In case of stoichiometric change, the NPC is presented as an example. Cell type-specific NPC stoichiometries imply a variable copy number of dynamic Nups, e.g., Gp210 or Nup214 and are shown in the right panel according to experimentally determined stoichiometries. The number of copies is shown for half a spoke, assuming an asymmetric distribution of Nup214 across the nuclear envelope plane. Alternatively, subunit switches as previously described for BAF (Lessard et al, 2007; Ho et al, 2009) and the proteasome (Noda et al, 2000; Murata et al, 2007) might occur. This scenario generally requires subunits to exist in multiple paralogs in order to be switched. Finally, subunits might compete for interfaces across multiple, overlapping protein complexes and re-distribute according to the variable abundance of the given complexes/subunits.