polyamine

Escherichia coli

学位:千大院薬博甲第106号

抄録:The mechanism of cell death by polyamine accumulation has been studied. The accumulation of spermidine leads to a decrease in cell viability and to a decrease in the synthesis of ribosome modulation factor (RMF) and of the cation-selective porin OmpC. RMF is involved in stabilization of ribosomes during the transition from exponential growth to the stationary phase in Escherichia coli, and it is necessary for cell viability. The enhancement of cell death by OmpC deficiency caused by RMF deficiency was investigated. The ompC mutant by itself did not affect protein synthesis or cell viability, but the double rmf ompC mutant produced a much larger decrease in protein synthesis and cell viability than did the single rmf mutant. There was also a decrease in the amount of ribosomes and in the Mg^<2+> content in the double rmf ompC mutant, and cell viability could be partially restored by the addition of Mg^<2+> to the growth medium. RMF deficiency was found to inhibit the synthesis of another cation-selective porin OmpF. Thus, the double rmf ompC mutant is deficient in both OmpC and OmpF, which probably accounts for the pronounced decrease in Mg^<2+> uptake in this mutant. The results indicate that both RMF and Mg^<2+>, acting through stabilization of ribosomes, are important for cell viability at the stationary growth phase. The mechanism of cell death caused by spermidine overaccumulation was further examined by using the spermidine acetyltransferase (SAT) gene-deficient mutant CAG2242. The growth of E. coli CAG2242 in LB medium was normal in the presence and absence of 2 mM or 4 mM spermidine.