The invention relates to compositions including polynucleotides encoding polypeptides which have been chemically modified by replacing the uridines with 1-methyl-pseudouridine to improve one or more of the stability and/or clearance in tissues, receptor uptake and/or kinetics, cellular access by the compositions, engagement with translational machinery, mRNA half-life, translation efficiency, immune evasion, protein production capacity, secretion efficiency, accessibility to circulation, protein half-life and/or modulation of a cell's status, function, and/or activity.