Recovery of the decrease in cell viability under polyamine deficiency by RMF and/or RpoS. A, E. coli MA261 cells carrying various plasmids were cultured in medium A with 0.5 mm isopropyl-β-d-thiogalactopyranoside in the presence and absence of 100 μg/ml putrescine. Cell viability was determined as described under “Experimental Procedures.” ●---●, MA261/pMW-lacRMF(WT) cultured with putrescine; ▴---▴, MA261/pMW-lacRMF(SD*)-RpoS(33CAG) cultured with putrescine; ●—●, MA261/pMW-lacRMF(WT) cultured without putrescine; □—□, MA261/pMW-lacRMF(SD*) cultured without putrescine; ◇—◇, MA261/pMW-lacRMF −6(C→G) cultured without putrescine; ○—○, MA261/ pMW-lacRMF −35(ΔU) cultured without putrescine; ▵—▵, MA261/pMW-lacRpoS(33CAG) cultured without putrescine; ▴—▴, MA261/pMW-lacRMF(SD*)-RpoS(33CAG) cultured without putrescine. B, level of RMF and RpoS in cells cultured with or without putrescine for 36 h was measured by Western blotting using 5 μg of protein. Values are means ± S.E. of triplicate determinations. ns, p > 0.05; *, p ≤ 0.05; **, p ≤ 0.01.