Enhancement of the Synthesis of RpoN, Cra and H-NS by Polyamines at the Level of Translation in Escherichia coli Cultured with Glucose and Glutamate

Graduate School of Pharmaceutical Sciences, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8675, Faculty of Pharmacy, Chiba Institute of Science, 15-8 Shiomi-cho, Choshi, Chiba 288-0025, Graduate School of Agriculture of Kinki University, 3327-204 Nakamachi, Nara 631-8505, and Department of Frontier Bioscience and Micro-Nano Technology Research Center, Hosei University, Koganei, Tokyo 184-8584, Japan

^* To whom correspondence should be addressed. Email: iga16077{at}p.chiba-u.ac.jp.

	Abstract

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 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 (A₅₄₀ = 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, 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 (³⁸), Cya, FecI (¹⁸), Fis, RpoN (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 two-fold were under the control of above seven polyamine modulon genes.