The murine grg (Groucho-related gene) products are believed to interact with 
transcription factors and repress transcription, thereby regulating cell 
proliferation and differentiation. Most proteins in the grg family contain all 
of the domains found in the Drosophila Groucho protein, including the S/P 
(Ser-Pro-rich) domain required for interaction with transcription factors and 
the WD40 domain, which is thought to interact with other proteins. However, at 
least two Grg proteins contain only the amino-terminal Q (glutamine-rich) 
domain. We examined whether the Q domain is used for dimerization between Grg 
proteins, using the yeast two-hybrid system and binding assays with glutathione 
S-transferase fusion proteins. We found that Grg proteins are able to dimerize 
through the Q domain and that dimerization requires a core of 50 amino acids. 
Surprisingly, the dimerization does not require the leucine zipper located 
within the Q domain.