title: Two mechanisms for putrescine-dependent transcriptional expression of the putrescine aminotransferase gene, ygjG, in Escherichia coli.
abstract: In this study, on evaluating the physiological function and mechanism of putrescine, we found that putrescine supplementation (1 mM) increases transcription of the putrescine aminotransferase gene, ygjG. Putrescine-dependent expression was confirmed by measuring β-galactosidase activity and with reverse transcription-polymerase chain reaction. To understand the role of putrescine in ygjG expression, we genetically characterized and found that a knockout mutation in an alternative sigma factor, rpoS, abolished putrescine-dependent ygjG-lacZ expression. In the rpoS mutant, RpoS overexpression complemented the mutant phenotype. However, RpoS overexpression induced ygjG-lacZ expression with putrescine supplementation but not without supplementation. We also found that the loss of putrescine-dependent ygjG-lacZ expression induced by rpoS was completely restored under nitrogen-starvation conditions. The putrescine-dependent expression of ygjG-lacZ under this condition was clearly dependent on another alternative sigma factor, rpoN, and its cognate activator ntrC. These results show that rpoS is required for putrescine-dependent ygjG-lacZ expression, but the effect of putrescine on this expression is not caused by simple modulation of RpoS synthesis. Putrescine-dependent expression of ygjG-lacZ was controlled by at least two sigma factors: rpoS under excess nitrogen conditions and rpoN under nitrogen-starvation conditions. These results suggest that putrescine plays an important role in the nitrogen regulation system.
authors.affiliation: Department of Biological Science, Sungkyunkwan University, Suwon, 440-746, Korea, youngskim@knue.ac.kr.
authors.forename: Young-Sik
authors.initials: YS
authors.lastname: Kim
authors.forename: Hyun-Chul
authors.initials: HC
authors.lastname: Shin
authors.forename: Jong-Ho
authors.initials: JH
authors.lastname: Lee
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects / Q000235:genetics*; D055786:Gene Knockout Techniques; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism; D011700:Putrescine / Q000494:pharmacology; D051877:RNA Polymerase Sigma 54 / Q000378:metabolism; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism; D000637:Transaminases / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D012808:Sigma Factor; C497751:rpoN protein, E coli; C069567:sigma factor KatF protein, Bacteria; D000637:Transaminases; C507750:YgjG protein, E coli; D051877:RNA Polymerase Sigma 54; D009584:Nitrogen; D011700:Putrescine