In a speG-disrupted Escherichia coli mutant, which cannot metabolize spermidine to acetylspermidine. addition of spermidine to the medium caused a decrease in cell viability at the late stationary phase of growth. There ere parallel decreases in the levels of ribosome modulation factor (RMF), the sigma(38) subunit of RNA polymerase, and the outer membrane protein C (OmpC). To clarify that these three proteins are strongly involved in cell viability, the rmf, rpoS (encoding sigma(38)), and ompC genes were disrupted. Viability of the triple mutant decreased to less than 1% of normal cells, The triple mutant had a reduced Cell viability compared to any combination of double mutants, which also had a reduced cell viability. The single roil and rpoS. but not ompC, mutant only slightly reduced cell viability. The results indicate that cooperative functions of these three proteins are neccssary for cell viability at the late stationary phase. The triple mutant had a reduced level of ribosomes and of intracellular cations. (C) 2002 Elsevier Science (USA). All rights reserved.