FIG. 4.

KMnO₄ reactivity of the origin region of a P1-derived plasmid, pSP102. The origin region is bounded by DnaA boxes and the five iterons and contains an internal A+T-rich region. The reactivity of the bottom strand is shown in four different hosts: PC2, BL21(DE3)/pET16b, BL21(DE3)/pST1, and DH5Δlac/pRLM109. The KMnO₄-reacted bases were visualized by primer extension. Localized increase of reactivity (bracket) is seen when the temperature of a dnaC(Ts) host (PC2) is raised to 42°C (lane 2), when P2 B is induced with IPTG (lanes 8 to 10), or when λ P protein is induced by temperature inactivation of cI857(Ts) repressor (lane 12). The first four lanes (G, A, T, and C) show the dideoxy sequencing reaction products of the P1 origin region.