Properties of a revertant of Escherichia coli viable in the presence of spermidine accumulation: Increase in L-glycerol 3-phosphate

Escherichia coli CAG2242 cells are deficient in the speG gene encoding sper midine acetyltransferase. When these cells were cultured in the presence of 0.5 to 4 mM spermidine, their viability was greatly decreased through the inhibition of protein synthesis by overaccumulation of spermidine, When the cells were cultured with a high concentration of spermidine (4 mM), a reve rtant strain was obtained. We found that a 55-kDa protein, glycerol kinase, was overexpressed in the revertant and that synthesis of a ribosome modula tion factor and the RNA polymerase sigma (38) subunit, factors important fo r cell viability, was increased in the revertant. Levels of L-glycerol 3-ph osphate also increased; in the revertant. Transformation of glpFK, which en codes a glycerol diffusion facilitator (glpF) and glycerol kinase (glpK), t o E, coil CAG2242 partially prevented the cell death caused by accumulation of spermidine. It was also found that L-glycerol 3-phosphate inhibited spe rmidine binding to ribosomes and attenuated the inhibition of protein synth esis caused by high concentrations of spermidine. These results indicate th at L-glycerol 3-phosphate reduces the binding of excess amounts of spermidi ne to ribosomes so that protein synthesis is recovered.