Acts as a transcriptional coactivator of ATF2. Binds to the N-terminal region of ATF2. Associates with the TFIID complex through interaction with TBP. Expressed mainly in pluripotent cells with expression rapidly down-regulated upon cell differentiation. First detected in the embryo at the blastocyst stage. Little or no expression detected in adult tissues. The leucine-zipper domain is required for coactivation activity. When this domain is deleted, the protein is able to stimulate transcription from a number of gene promoters. Phosphorylated.