Nanog is a newly identified homeodomain gene that functions to sustain the 
pluripotency of embryonic stem cells. However, the molecular mechanism through 
which nanog regulates stem cell pluripotency remains unknown. Mouse nanog 
encodes a polypeptide of 305 residues with a divergent homeodomain similar to 
those in the NK-2 family. The rest of nanog contains no apparent homology to any 
known proteins characterized so far. It is hypothesized that nanog encodes a 
transcription factor that regulates stem cell pluripotency by switching on or 
off target genes. To test this hypothesis, we constructed fusion proteins 
between nanog and DNA binding domains of the yeast transcription factor Gal4 and 
tested the transactivation potentials of these constructs. Our data demonstrate 
that both regions N- and C- terminal to the homeodomain have transcription 
activities. Despite the fact that it contains no apparent transactivation 
motifs, the C-terminal domain is about 7 times as active as the N-terminal one. 
This unique arrangement of dual transactivators may confer nanog the flexibility 
and specificity to regulate downstream genes critical for both pluripotency and 
differentiation of stem cells.