Fig. 1. The N-terminal domain of Bcd inhibits its own activity. (A) A truncated Bcd derivative [Bcd(92-489)] exhibits an activity higher than that of the full-length protein. CAT assay results from Drosophila S2 cells that were transfected with the hb-CAT reporter plasmid and effector plasmids that express Bcd(1-489) or Bcd(92-489). The CAT activity for wild-type Bcd (expressed from 1 µg transfected effector DNA) on this reporter is arbitrarily assigned as 100 throughout this report. The standard error (s.e.m.) for the activity of Bcd(92-489) on hb-CAT was 23%. While the representative CAT assay results shown here were obtained with the same length of enzymatic reaction time (30 minutes), accurate CAT activities (as measured numbers) were obtained with different lengths of reaction time to keep the assays in the linear range. (B) Delineating the self-inhibitory domain of Bcd. Shown are CAT activities for the N-terminal deletion derivatives of Bcd in transient transfection assays on the hb-CAT reporter. The homeodomain (HD) of Bcd (residues 92-151) is marked.