Modulation of cellular functions by polyamines through polyamine interaction with RNA and proteins

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1.Synthesis of specific proteins such as OppA, Cya and RpoS (σ^<38>), which are important for cell growth and viability, is stimulated by polyamines at the level of translation in E. coli. In this study, we found that synthesis of Fecl and Fis was also stimulated by polyamines at the level of translation. Fecl and Fis proteins enhance expression of mRNAs involved in iron uptake and energy metabolism, and of rRNA and some tRNAs. When the Shine-Dalgarno (SD) sequences were created at the normal position on these mRNAs, protein synthesis was no longer influenced by polyamines. Thus, the common characteristic of these mRNAs was to have a weak or ineffective SD sequence. We propose that a group of genes whose expression is enhanced by polyamines at the level of translation is referred to as a "polyamine modulon".2.Effect of polyamines on frameshift during translation in E. coli was studied. Frameshift at the 26th termination codon in the open reading frame of RF2 mRNA was stimulated by polyamines in in vivo and in vitro experimental systems. Stimulation occurred at the early logarithmic phase of cell growth, in which the ratio of RF2 mRNA to RF2 protein is high. Polyamines functioned at the decoding site on ribosomes.3.Cycling of polyamines (spermine and spermidine) in the brain was examined by measuring polyamine transport in synaptic vesicles, synaptosomes and glial cells, and the release of spermine from hippocampal slices. It was found that membrane potential-dependent polyamine transport systems exist in synaptosomes and glial cells, and a proton gradient-dependent polyamine transport system exists in synaptic vesicles. Spermine was found to be accumulated in synaptic vesicles and was released from rat hippocampal slices by depeolarization using a high concentration of KCl. Polyamines, in particular spermine, may function as neuromodulators in the brain.