Figure 2.

Repression of a lacZ reporter gene by a fusion protein SopB(1–323)Gal4. (A) The levels of β-galactosidase 2 hr after the addition of the indicated amounts of IPTG to cells harboring a pair of plasmids depicted in Fig. 1 (open squares) or to cells harboring the same pair of plasmids, except that the lacZ reporter plasmid carries no Gal4-binding site (closed squares). The levels of β-galactosidase in cells not exposed to IPTG were not significantly different from those induced with 0.001 mM IPTG. (B–D) Measurements of the plasmid copy numbers (B), the concentration of SopB(1–323)Gal4 fusion protein (C), and β-galactosidase level (D) at various times after the addition of IPTG to 1 mM. Aliquots (1 ml each) of cells harboring the fusion protein expression plasmid and the lacZ reporter plasmid depicted in Fig. 1 were sampled at the indicated times. The fastest migrating band in each sample run in (B) was a linearized 3-kbp plasmid, which was added to the cell suspensions before lysis to monitor the recovery of plasmid DNA.