Ser276-Gly510. Two N-terminal tags, His-tag and T7-tag. MW: 29.3 kDa (Predicted Molecular Mass), 34 & 42 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. Recombinant Sperm Specific Antigen 2 (SSFA2) is a recombinant protein from Human. It is produced in E.coli using Prokaryotic expression.