RESUMEN
Proteins whose synthesis is enhanced by polyamines at the level of translation were identified in a polyamine-requiring mutant cultured in the presence of 0.1% glucose and 0.02% glutamate instead of 0.4% glucose as an energy source. Under these conditions, enhancement of cell growth by polyamines was almost the same as that in the presence of 0.4% glucose. It was found that synthesis of RpoN, Cra, and H-NS was enhanced by polyamines at the level of translation at the early logarithmic phase of growth (A(540) of 0.15). The effects of polyamines on synthesis of RpoN, H-NS, and Cra were due to the existence of unusual Shine-Dalgarno sequences (RpoN and H-NS) and an inefficient GUG initiation codon (Cra) in their mRNAs. Thus, rpoN, cra, and hns genes were identified as new members of the polyamine modulon. Because most of the polyamine modulon genes thus far identified encode transcription factors (RpoS [sigma(38)], Cya, FecI [sigma(18)], Fis, RpoN [sigma(54)], Cra, and H-NS), DNA microarray analysis of mRNA expressed in cells was performed. At the early logarithmic phase of growth, a total of 97 species of mRNAs that were up-regulated by polyamines more than twofold were under the control of seven polyamine modulon genes mentioned above.
Asunto(s)
Proteínas de Escherichia coli/metabolismo , Escherichia coli/crecimiento & desarrollo , Escherichia coli/metabolismo , Regulación Bacteriana de la Expresión Génica , Poliaminas/farmacología , Biosíntesis de Proteínas , Proteínas Bacterianas/química , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Codón Iniciador , Proteínas de Unión al ADN/química , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Escherichia coli/efectos de los fármacos , Escherichia coli/genética , Proteínas de Escherichia coli/química , Proteínas de Escherichia coli/genética , Glucosa/metabolismo , Glucosa/farmacología , Ácido Glutámico/metabolismo , Ácido Glutámico/farmacología , Análisis de Secuencia por Matrices de Oligonucleótidos , Poliaminas/metabolismo , ARN Polimerasa Sigma 54/química , ARN Polimerasa Sigma 54/genética , ARN Polimerasa Sigma 54/metabolismo , ARN Bacteriano/química , ARN Bacteriano/genética , ARN Bacteriano/metabolismo , ARN Mensajero/química , ARN Mensajero/genética , ARN Mensajero/metabolismo , Proteínas Represoras/química , Proteínas Represoras/genética , Proteínas Represoras/metabolismoRESUMEN
We reported previously that the synthesis of specific proteins such as OppA, Cya, and RpoS (sigma(38)), which are important for cell growth and viability, is stimulated by polyamines at the level of translation. In this study we found that the synthesis of FecI and Fis was also stimulated by polyamines at the level of translation. The FecI and Fis proteins enhance the expression of mRNAs that are involved in iron uptake and energy metabolism and the expression of rRNA and some tRNAs. The Shine-Dalgarno (SD) sequence of their mRNAs was not obvious or was not located at the usual position. When the 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 be referred to as a "polyamine modulon." By DNA microarray, we found that 309 of 2,742 mRNA species were upregulated by polyamines. Among the 309 up-regulated genes, transcriptional enhancement of at least 58 genes might be attributable to increased levels of the transcription factors Cya, RpoS, FecI, and Fis, which are all organized in the polyamine modulon. This unifying molecular mechanism is proposed to underlie the physiological role of polyamines in controlling the growth of Escherichia coli.