LIN28 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. Subsequently, LIN28 expression has been used to generate iPS cells.
Human elongation factor-1 alpha (EF-1 alpha) is a constitutive promoter of human origin that can be used to drive ectopic gene expression in various in vitro and in vivo contexts. EF-1 alpha (or EF1a) is often useful in conditions where other promoters (such as CMV) have diminished activity or have been silenced (as in embryonic stem cells).