Loss of tyrosinase expression in E. coli JM109 (pMFvpt). The cells were grown in shake flasks at 32°C and induced with 1.0 mM IPTG. (A) Time profile of cell growth and tyrosinase activity of E. coli JM109 freshly transformed with pMFvpt and E. coli JM109 (pMFvpt) stored at 4°C for 24 h. The arrow indicates the onset of IPTG induction. (B) SDS-PAGE of total proteins prepared from E. coli JM109 (pMFvpt) cells. Samples were taken after 4 h just before induction (lanes 1 and 5), after 7 h (3 h induction, lanes 2 and 6), after 8 h (4 h induction, lanes 3 and 7), and after 24 h (20 h induction, lanes 4 and 8). Lanes 1–4, samples of freshly transformed E. coli JM109 (pMFvpt); Lanes 5–8, samples of 24 h old E. coli JM109 (pMFvpt). The arrow indicates the position of tyrosinase in the gel. Molecular weight standards are shown on the left.