Source : Sf9 insect cells. Recombinant TOP1 70kDa protein is an enzyme fragment having a molecular mass of 69,199 Dalton (pH 9.4). TOP1 70kDa protein is fused to a hexa-histidine purification tag. TOP1 is an important nuclear enzyme that interconverts supercoiled DNA to the necessary topological conformations for standard DNA replication and transcription. TOP1 is the target antigen for TOP1 autoantibodies. TOP1 antibodies are a specific marker in scleroderma patients (specificity 98-100%) and are related with the existence of diffuse skin involvement and pulmonary fibrosis. In human tissues top1 enzyme is primarily synthesized as a protein with a molecular weight of 100-kDa. Most of this precursor is then proteolytically processed to a 70-kDa size, from which the TOP1 antigen has derived its name.