Ala28-Arg193. N-terminal His-tag. MW: 20.0 kDa (Predicted Molecular Mass), 33-40 kDa (Accurate Molecular Mass as determined by SDS-PAGE) Possible reasons why the actual band size differs from the predicted band size: 1. Splice variants. Alternative splicing may create different sized proteins from the same gene. 2. Relative charge. The composition of amino acids may affect the charge of the protein. 3. Post-translational modification. Phosphorylation, glycoslyation, methylation etc. may affect the band size. 4. Post-translational cleavage. Many proteins are synthesised as pro-proteins, and then cleaved to give the active form. 5. Polymerisation of the target protein. Dimerisation, multimerisation etc. will increase the band size observed. Erythropoietin Protein (Recombinant) is an active Human protein. It is produced in 293F cells using Eukaryotic expression.