CreER / CreERT2 (Tamoxifen-Inducible Cre)

CreER is Cre recombinase fused to a mutated ligand-binding domain of the estrogen receptor, which adds temporal control to the spatial control a tissue-specific promoter already provides. The fusion protein is held in the cytoplasm bound to heat shock protein 90 (HSP90). Binding of a synthetic steroid - tamoxifen or 4-hydroxytamoxifen (4-OHT) - disrupts the HSP90 interaction, allowing the protein to translocate to the nucleus, engage loxP sites and recombine them. Tamoxifen is typically administered by intraperitoneal injection.

CreERT2 is an improved version roughly ten-fold more sensitive to 4-OHT in vivo than the original CreERT, and is generally the preferred choice.