Abstract
Members of polyamine modulon whose synthesis is enhanced at the level of translation were looked for under oxidative stress conditions caused by 0.6 μM K2TeO3. When an Escherichia coli polyamine-requiring mutant MA261 was cultured in the presence of K2TeO3, the degree of polyamine stimulation of cell growth was greater than in cells cultured in the absence of K2TeO3. Under these conditions, synthesis of SoxR, a transcriptional factor for expression of the superoxide response regulon, EmrR, a negative transcriptional factor for expression of the genes for drug excretion proteins, EmrA and EmrB, and of GshA, γ-glutamylcysteine synthetase necessary for glutathione (GSH) synthesis, were stimulated by polyamines at the level of translation. Polyamine stimulation of SoxR and EmrR synthesis was dependent on the existence of an unusually located Shine-Dalgarno (SD) sequence in soxR and emrR mRNAs. Polyamine stimulation of GshA synthesis was due to the existence of the inefficient initiation codon UUG instead of AUG. Polyamine stimulation of the synthesis of EmrR was mainly observed at the logarithmic phase of growth, while that of the synthesis of SoxR and GshA was at the stationary phase. These results strongly suggest that polyamines are involved in easing of oxidative stress through stimulation of synthesis of SoxR, EmrR and GshA together with RpoS, previously found as a member of polyamine modulon at the stationary phase.
Highlights
Polyamines, aliphatic cations present in almost all living organisms, are necessary for normal cell growth [1]
We looked for members of the polyamine modulon involved in oxidative stress
It was found that the synthesis of SoxR, EmrR and glutamylcysteine synthetase (GshA) was stimulated by polyamines at the level of translation, indicating that genes encoding soxR, emrR and gshA are members of polyamine modulon
Summary
Polyamines (putrescine, spermidine and spermine), aliphatic cations present in almost all living organisms, are necessary for normal cell growth [1]. Polyamine Modulon under Oxidative Stress Conditions nucleic acids and exist mostly as polyamine-RNA complexes in cells [2, 3], their proliferative effects are presumed to be caused by changes in RNA function. In this context, it has been reported that polyamines stimulate the synthesis of some proteins in vitro [4, 5], increase the fidelity of protein synthesis [6, 7], and induce in vivo assembly of 30S ribosomal subunits [8, 9], suggesting that polyamines regulate protein synthesis at several different steps. The functions of 17 proteins encoded by polyamines were summarized [14], indicating that polyamines increase cell growth as well as cell viability
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