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Posttranscriptional Activation of the Transcriptional Activator Rob by Dipyridyl in Escherichia coli. Judah L. Rosner, 2002.The transcriptional activator Rob consists of an N-terminal domain (NTD) of 120 amino acids responsible for DNA binding and promoter activation and a C-terminal domain (CTD) of 169 amino acids of unknown function . Although several thousand molecules of Rob are normally present per Escherichia coli cell, they activate promoters of the rob regulon poorly . We report here that in cells treated with either 2,2"- or 4,4"-dipyridyl (the latter is not a metal chelator), Rob-mediated transcription of various rob regulon promoters was increased substantially . A small, growth-phase-dependent effect of dipyridyl on the rob promoter was observed . However, dipyridyl enhanced Rob's activity even when rob was regulated by a heterologous (lac) promoter showing that the action of dipyridyl is mainly posttranscriptional . Mutants lacking from 30 to 166 of the C-terminal amino acids of Rob had basal levels of activity similar to that of wild-type cells, but dipyridyl treatment did not enhance this activity . Thus, the CTD is not an inhibitor of Rob but is required for activation of Rob by dipyridyl . In contrast to its relatively low activity in vivo, Rob binding to cognate DNA and activation of transcription in vitro is similar to that of MarA, which has a homologous NTD but no CTD . In vitro nuclear magnetic resonance studies demonstrated that 2,2"-dipyridyl binds to Rob but not to the CTD-truncated Rob or to MarA, suggesting that the effect of dipyridyl on Rob is direct . Thus, it appears that Rob can be converted from a low activity state to a high-activity state by a CTD-mediated mechanism in vivo or by purification in vitro . DNA Microarray Analysis of Redox-Responsive Genes in the Genome of the Cyanobacterium Synechocystis sp . Strain PCC 6803. Yukako Hihara, 2003.Whole-genome DNA microarrays were used to evaluate the effect of the redox state of the photosynthetic electron transport chain on gene expression in Synechocystis sp . strain PCC 6803 . Two specific inhibitors of electron transport, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), were added to the cultures, and changes in accumulation of transcripts were examined . About 140 genes were highlighted as reproducibly affected by the change in the redox state of the photosynthetic electron transport chain . It was shown that some stress-responsive genes but not photosynthetic genes were under the control of the redox state of the plastoquinone pool in Synechocystis sp . strain PCC 6803 . Production of a Polyunsaturated Isoprenoid Wax Ester during Aerobic Metabolism of Squalene by Marinobacter squalenivorans sp . nov.. Jean-François Rontani, 2003.This paper describes the production of 5,9,13-trimethyltetradeca-4E,8E,12-trienyl-5,9,13-trimethyltetradeca-4E,8E,12-trienoate during the aerobic degradation of squalene by a Marinobacter strain, 2Asq64, isolated from the marine environment . A pathway involving initial cleavage of the C10-C11 or C14-C15 double bonds of the squalene molecule is proposed to explain the formation of this polyunsaturated isoprenoid wax ester . The isoprenoid wax ester content reached 1.1% of the degraded squalene at the mid-exponential growth phase and then decreased during the stationary phase . The wax ester content increased by approximately threefold in N-limited cultures, in which the ammonium concentration corresponds to conditions often found in marine sediments . This suggests that the bacterial formation of isoprenoid wax esters might be favored in such environments . The bacterial strain is then characterized as a member of a new species, for which we propose the name Marinobacter squalenivorans sp . nov .
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