Some aspects of this disclosure relate to systems, apparatuses, compositions (e.g., isolated nucleic acids and vectors), and methods for improving the stability and/or solubility of proteins evolved using phage-assisted continuous evolution (PACE). In some embodiments, vectors described herein comprise nucleic acids encoding selection systems (e.g., positive and/or negative selection systems) that link expression of genes required for production of infectious phage particles to a desirable physiochemical (e.g., stability or solubility) and/or desired function of an evolved protein.