UTF1 is a transcriptional coactivator expressed in pluripotent embryonic stem cells and extra-embryonic cells. Upon activation by Oct-3/4, UTF1 may be responsible for the rapid proliferation and tumorigenic properties of embryonic stem cells. Sox2 is also part of the Oct-3/4-containing complex able to bind the regulatory region of UTF1. UTF1 acts as a transcriptional coactivator of ATF2 and it binds to the N-terminal region of ATF2. Associates with the TFIID complex through interaction with TBP.