CNOT9, the mammalian ortholog of Rcd1 and Caf40 (Collart and Timmers, 2004), acts as a transcriptional cofactor that plays a critical role in RA-induced differentiation of F9 embryonic teratocarcinoma cells and in lung development, through an association with a transcription complex containing activation transcription factor-2 (ATF-2) and RA receptors (RARs) in an RA-dependent fashion (Hiroi et al., 2002). Here, ATF2 is linked to teratocarcinoma.