## 2 Results
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Mechanism**} & **Increase in Cell Growth** & \begin{tabular}{c} **Increase in Cell Growth** \\ **Growth under** \\ **Heat Shock Stress** \\ \end{tabular} & \begin{tabular}{c} **Increase in Cell Growth** \\ **and Viability under** \\ **Oxidative Stress** \\ \end{tabular} & \begin{tabular}{c} **Increase in** \\ **Cell Viability** \\ **Cell Viability** \\ \end{tabular} \\ \hline \begin{tabular}{c} (1) Long distance between \\ the SD sequence and \\ initiation codon AUG \\ \end{tabular} & \begin{tabular}{c} Fis [20] \\ Fool (\(\sigma^{54}\)) [21] \\ OppA [22] \\ H-NS [21] \\ \end{tabular} & \begin{tabular}{c} RpoE (\(\sigma^{24}\)) [23] \\ StpA [23] \\ H-NS [21] \\ \end{tabular} & \begin{tabular}{c} SoxR [24] \\ EmrR [24] \\ CpxR [27] \\ \end{tabular} \\ \hline \begin{tabular}{c} (2) Initiation on an inefficient \\ initiation codon (normal \\ position of the SD sequence \\ from AUG) \\ \end{tabular} & \begin{tabular}{c} Cra [21] \\ Cya [28] \\ \end{tabular} & \begin{tabular}{c} GshA [24] \\ \end{tabular} & \begin{tabular}{c} RRF [27] \\ SpoT [26] \\ UvrY [27] \\ \end{tabular} \\ \hline \begin{tabular}{c} (3) Suppression or +1 \\ frameshifting on a nonsense \\ codon (normal position of \\ the SD sequence from AUG) \\ \end{tabular} & \
\begin{tabular}{c} RF2 [29] \\ \end{tabular} &
\begin{tabular}{c} RpoS (\(\sigma^{38}\)) [30] \\ \end{tabular} & RpoS (\(\sigma^{38}\)) [30] \\ \end{tabular}
\end{table} 
Table 1: Three mechanisms of polyamine stimulation of the protein synthesis encoded by polyamine modulon. encoded by members of polyamine modulon that have a normally positioned SD sequence in their mRNAs was not inhibited significantly by excess SPD. Levels of mRNAs encoded by polyamine modulon were not influenced by excess SPD (Figure S1). These results indicate that the synthesis of proteins encoded by polyamine modulon is inhibited by excess SPD at the translational level. As a control, the effect of SPD on RpoD (\(\sigma^{70}\) transcriptional factor, a major \(\sigma\) factor) synthesis was examined, and excess SPD did not reduce RpoD synthesis significantly. Considering the protein synthesized at the logarithmic phase, synthesis of H-NS was not influenced by excess SPD. H-NS is a member of nucleoid-associated DNA-binding proteins, including StpA. H-NS and StpA share similar functions, but are regulated differently by growth temperature. It was reported that the level of H-NS decreased and that of StpA increased at 42 \({}^{\circ}\)C compared to those protein levels at 37 \({}^{\circ}\)C [32]. Thus, we next determined whether the syntheses of the proteins encoded by members of polyamine modulon were altered by excess SPD under various growth conditions, such as elevated growth temperature. As shown in Figure 2A, the reduction of growth rate of _E. coli_ CAG2242 by 4 mM SPD was not altered at 42 \({}^{\circ}\)C compared to 37 \({}^{\circ}\)C. However, the lag phase of growth of _E. coli_ CAG2242 in the presence of 4 mM SPD at 42 \({}^{\circ}\)C was prolonged, and the yield was less at 12 h. Therefore, growth of _E. coli_ CAG2242 in the presence of 4 mM SPD at 42 \({}^{\circ}\)C was slightly slower than at 37 \({}^{\circ}\)C. These results indicate  
Figure 1: Inhibition of cell growth of _E. coli_ CAG2242 by excess SPD. Cell growth of _E. coli_ CAG2242 cells with or without 4 mM SPD. Values are means of triplicate determinations. Error bars are within the symbol size (**A**). Polyamine contents in cells harvested at \(\text{A}_{540}\) of 0.2 and 0.6 were measured as described under “Materials and Methods” (**B**). The levels of Fis, Fecl (\(\sigma^{18}\)), RpoD (\(\sigma^{54}\)), OppA, H-NS, Cra, Cya, and RF2 were measured together with a control protein, RpoD (\(\sigma^{70}\)), by Western blotting (**C**). Values are means \(\pm\) S.E. of triplicate determinations. Student’s \(t\)-test was performed for the values obtained in the presence of SPD versus in the absence of SPD.