Fig. 1. Six3 and members of the Groucho family of corepressors. (A) The pc97-Six3 and pc86-Grg5 constructs used in the yeast transformation assay. Gal4-DB, Gal4 DNA-binding domain; SD, Six domain; HD, homeodomain; Gal4-AD, Gal4 activation domain; Q, glutamine-rich domain; GP, glycine and proline-rich domain. (B) Comparison of murine Grg family members with Drosophila Groucho protein. Mouse Grg5 lacks the CcN domain (potential phosphorylation sites for casein kinase II and cdc2), SP domain (serine- and proline-rich) and WD40 repeat domain (40 amino acid repeats separated by tryptophan and aspartic acid), but it contains the Q and GP domains. The Q domain of mouse Grg5 shares as much as 64% amino acid identity with Drosophila Groucho.