Fig. 4. The self-inhibitory domain of Bcd works as an independent module. (A) Deletion derivatives of Bcd, either wild-type or Bcd(A52-56), were used in transient transfection assays. The derivative shown at the bottom (6) contains the DNA-binding domain of GAL4 (residues 2-94) in place of the homeodomain of Bcd. The activities, shown in the table, of the wild-type and mutant forms of this hybrid protein were obtained from the GAL4-CAT reporter gene, which contains five GAL4 sites upstream of the CAT gene. All other derivatives were assayed on the hb-CAT reporter gene. *The activity of the wild type Bcd-GAL4(2-94) hybrid protein on the GAL4-CAT reporter is assigned as 100, a standard for the relative CAT activity shown in B. (B) The self-inhibitory domain of Bcd can repress the activity of heterologous activators. Activities of hybrid activators that contain the DNA-binding domain of GAL4 (residues 1-147) fused to bacterially derived activation sequences (B6 and B42) are shown in the table. In addition, the first 91 amino acids of Bcd, either wild type or Bcd(A52-56), were attached to the N termini of these activators. The column designated –Bcd shows results of an activator lacking any Bcd sequence.