LIN28A is a microRNA-binding protein that has been shown to bind the let-7 pre-microRNA and block production of mature let-7 in embryonic stem cells. This activity appears to preserve undifferentiated state of stem cells. LIN28A has been used to generate iPS cells. LIN28A lentivirus (EF1a, Puro) expresses human LIN28 under the control of the EF1a promoter with puromycin as a selection marker.