Polyamine content of nucleated and enucleated Escherichia coli cells

Endogenous polyamine function--the RNA perspective

Recent progress with techniques for monitoring RNA structure in cells such as ‘DMS-Seq’ and ‘Structure-Seq’ suggests that a new era of RNA structure-function exploration is on the horizon. This will also include systematic investigation of the factors required for the structural integrity of RNA. In this context, much evidence accumulated over 50 years suggests that polyamines play important roles as modulators of RNA structure. Here, we summarize and discuss recent literature relating to the roles of these small endogenous molecules in RNA function. We have included studies directed at understanding the binding interactions of polyamines with polynucleotides, tRNA, rRNA, mRNA and ribozymes using chemical, biochemical and spectroscopic tools. In brief, polyamines bind RNA in a sequence-selective fashion and induce changes in RNA structure in context-dependent manners. In some cases the functional consequences of these interactions have been observed in cells. Most notably, polyamine-mediated effects on RNA are frequently distinct from those of divalent cations (i.e. Mg²⁺) confirming their roles as independent molecular entities which help drive RNA-mediated processes.

Nucleoside triphosphate regeneration decreases the frequency of translation errors

The addition of naturally occurring polyamines and inorganic ions to an in vitro protein-synthesizing system improved the extent and fidelity of translation. In such an optimized system, regeneration of the nucleoside triphosphates with phosphoenolpyruvate and pyruvate kinase (ATP:pyruvate 2-O-phosphotransferase, EC 2.7.1.40) reduced further the missense error frequency to the in vivo level as well as enhanced the extent of translation. The effect of nucleoside triphosphate regeneration was shown to be due primarily to the increase in the ratio of adenosine and guanosine triphosphates to their hydrolysis products and only marginally due to the increase in the absolute concentrations of the nucleoside triphosphates.

Spermidine-Deoxyribonucleic acid interaction in vitro and in Escherichia coli

The binding of spermidine to deoxyribonucleic acid (DNA) was studied by equilibrium dialysis in a wide range of salt concentrations. The association constants ranged from 6 x 10(5) M-1 in 1 mM sodium cacodylate, pH 7.5, to 3 x 10(2) M-1 in 0.3 M NaCl. MgCl2 reduced spermidine-DNA interaction even more than NaCl so that in moderate-ionic-strength solutions (0.3 M NaCl, 0.002 M MgCl2) there was little detectable binding. Low-ionic-strength media were used to isolate DNA from Escherichia coli by a method shown to minimize loss of spermidine from the DNA. Considerable spermidine was associated with E. coli DNA, but control experiments indicated that complex formation had taken place during or after lysis of the cells. Exogenous DNA or ribonucleic acid added to spheroplasts at the time of their lysis caused most of the cellular spermidine to be scavenged by the extra nucleic acid. The data suggest that spermidine is relatively free in the cell and thereby capable of strong (high-affinity) associations with nucleic acids only after the ionic strength of the cell environment is lowered.

Polyamine levels during growth, sporulation, and spore germination of Bacillus megaterium

Spermidine was the major (>95%) polyamine of Bacillus megaterium in all stages of growth, although it could be replaced completely by spermine. Log-phase cells had 40 to 50% as much spermidine, based on ribonucleic acid (RNA) content, as did either stationary-phase cells or dormant spores; similar results were obtained in three other bacilli including an asporogenous mutant. Polyamine levels were essentially the same in B. megaterium grown in rich or poor media, or in media of high or low ionic strength. Polyamine levels were elevated three- to sixfold by exogenous spermidine without a major effect on growth, sporulation, or subsequent spore germination. During germination, the absolute amount of spermidine remained constant for almost 2 h until net RNA synthesis had lowered the polyamine/RNA ratio to a value close to that in log-phase cells. At this time, the spermidine level began to rise, and thereafter spermidine and RNA increased in parallel. This parallel relationship between the spermidine and RNA levels was abolished by actinomycin D, but not by chloramphenicol.

Presence of nuclear bodies in some minicells of Escherichia coli

Electron microscopy of serial sections of Escherichia coli K-12 (P678-54) revealed that some "minicells" contain nuclear bodies.