Figure 1.

The effect of λRexB on the P1 addiction system. (a) E. coli strain MC4100 was transformed with pGB2ts or pGB2ts∷phd-doc, and transformants were selected after 48 hr at 30°C on LB agar plates supplemented with spectinomycin (100 μg/ml). The postsegregational killing effect of the phd-doc addiction module was studied by growing the bacteria on LB agar plates at 30°C or 42°C (19). Cells carrying pGB2ts grew at both 30°C and 42°C. On the other hand, wild-type cells carrying pGB2ts∷phd-doc also grew at 30°C but died at 42°C. After testing the P1 addiction system in this way, MC4100/pGB2ts∷phd-doc cells were transformed either with pBR322 (C for control), pRS10 (rexB), pRS11(rexB_UAG), or pRS12(rexB_UAA). The doubly transformed cells were selected at 30°C on plates containing spectinomycin and ampicillin and subsequently grown at either 30°C or 42°C on LB plates with ampicillin only for 24 hr. The results of last step are shown in a. In b, E. coli MC4100 was lysogenized with λ or with λrexB∷Ω. The cells were then transformed with pGB2ts∷phd-doc. b shows transformed E. coli grown on LB plates for 24 hr at either 30°C or 42°C.