FIG. 1.

Effect of overproduction of ɛ on the ability of elevated levels of the umuDC gene products to interfere with DNA replication at the nonpermissive temperature of 30°C in E. coli GW8025 [lexA300(Def)::spec ΔumuDC595::cat recA441 xyl-5 mtl-1 galK2 rpsL31 kdgK51 Δ(argF-lacU)169 lacY1 tsx-33 supE44 thi-1 leuB6 hisG4(Oc) mgl-51 argE3(Oc) rfbD1 ara-14 thr-1 qsr′ qin-111 sulA11 ilvD(Ts) λ⁻ Rac⁻] (25). [methyl-³H]thymidine incorporation (counts per minute of [methyl-³H]thymidine per unit of optical density at 600 nM × 10⁻⁴) was measured as described elsewhere (2) after incubation for 10 min at 42°C (A) or either 10 min (B) or 2 h (C) following a shift in the incubation temperature from 42°C to 30°C. Note the differences in scales for [methyl-³H] thymidine incorporation at 30 and 42°C. Symbols: □, GW8025(pBR322kan); ■, GW8025(pSU38-DC)(pHN1) (minus IPTG); ○, GW8025(pSU38-DC)(pHN1) (plus 0.1 mM IPTG).