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Journal of Bacteriology, September 2009, p. 5348-5357, Vol. 191, No. 17
0021-9193/09/$08.00+0     doi:10.1128/JB.00387-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Enhancement of the Synthesis of RpoE and StpA by Polyamines at the Level of Translation in Escherichia coli under Heat Shock Conditions{triangledown}

Yusuke Terui,1 Kyohei Higashi,2,3 Yuzuru Tabei,1 Hideyuki Tomitori,1 Kaneyoshi Yamamoto,4 Akira Ishihama,4 Kazuei Igarashi,2,3 and Keiko Kashiwagi1*

Faculty of Pharmacy, Chiba Institute of Science, 15-8 Shiomi-cho, Choshi, Chiba 288-0025,1 Graduate School of Pharmaceutical Sciences, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8675,2 Amine Pharma Research Institute, Innovation Plaza at Chiba University, 1-8-15 Inohana, Chuo-ku, Chiba 260-0856,3 Department of Frontier Bioscience, Hosei University, Koganei, Tokyo 184-8584, Japan4

Received 21 March 2009/ Accepted 13 June 2009

Proteins whose synthesis is enhanced by polyamines at the level of translation were identified with a polyamine-requiring mutant cultured in the presence of 0.1% glucose and 0.02% glutamate at 42°C. Polyamines had a greater effect on cell growth at 42°C than at 37°C. At 42°C, the synthesis of RpoE ({sigma}24) and StpA, which are involved in the transcription of a number of heat shock response genes, was stimulated by polyamines at the level of translation. In the rpoE and stpA mRNAs, a Shine-Dalgarno (SD) sequence is located at 13 and 12 nucleotides, respectively, upstream of the initiation codon AUG. When the SD sequences were moved to the more common position 7 nucleotides upstream of the initiation codon AUG, the degree of polyamine stimulation was reduced, although the level of RpoE and StpA synthesis was markedly increased. The mechanism underlying polyamine stimulation of RpoE synthesis was then studied. Polyamine stimulation of RpoE synthesis was reduced by changing the bulged-out structure in the initiation site of rpoE mRNA, although the level of RpoE synthesis increased. A selective structural change of this bulged-out region induced by spermidine at 42°C was observed by circular dichroism. Polyamine stimulation of fMet-tRNA binding to ribosomes at 42°C also disappeared by changing the bulged-out structure in the initiation site of rpoE mRNA. The results suggest that polyamines enhance the synthesis of RpoE by changing the bulged-out structure in the initiation site of rpoE mRNA.

* Corresponding author. Mailing address: Faculty of Pharmacy, Chiba Institute of Science, 15-8 Shiomi-cho, Choshi, Chiba 288-0025, Japan. Phone: 81-479-30-4687. Fax: 81-479-30-4704. E-mail: kkashiwagi{at}cis.ac.jp

{triangledown} Published ahead of print on 19 June 2009.

Journal of Bacteriology, September 2009, p. 5348-5357, Vol. 191, No. 17
0021-9193/09/$08.00+0     doi:10.1128/JB.00387-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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