We investigate the relationship between mRNA expression levels and protein aggregation propensities at the proteomic level, and find that these quantities exhibit a significant correlation when they are averaged across subcellular localisations. In order to investigate this phenomenon, we study the dependence of mRNA expression levels and protein aggregation propensities on the volume of the corresponding subcellular localisations, finding that proteins tend to be increasingly more abundant and more soluble with decreasing volumes of their subcellular localisations. These results indicate that the maintenance of protein solubility plays an even greater role than previously thought in sustaining protein homeostasis.