(E) Analysis of the in vivo kinetics of formation and fate of MgtE cleavage products. B. subtilis strains expressing YqgP or its S288A mutant (strains BTM78; 501 and 502, Table EV2) in the presence or absence of endogenous FtsH protease (strains BTM795, BTM796 and BTM797, Table EV2) were cultured in LB medium and at early exponential phase, after having been expressing YqgP variants for 30 min, were either left grown untreated (as a control with ongoing translation) or treated with 20 μg/mL tetracycline to stop proteosynthesis (translation shut-off). At given time intervals afterwards, all cultures were analysed by α-MgtE western blotting with near infrared detection. Equal cell number (judged by OD600) was loaded into each lane. Black arrow marks full-length MgtE, red full arrows mark YqgP-dependent and red open arrows mark YqgP.S288A-dependent cleavage product of MgtE. 