Regulation of RRNA Expression in Escherichia Coli Under Conditions of Changing Growth Phase and Growth Rate PDF Download
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Author: Jeremy Alexander Appleman
Publisher:
ISBN:
Category :
Languages : en
Pages : 298
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Author: Jeremy Alexander Appleman
Publisher:
ISBN:
Category :
Languages : en
Pages : 298
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Author: Chenglu Chen
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Upon encountering stress conditions, cells must rapidly alter their gene expression and re-model their RNA complement to deal with the changing environment. As a consequence, both new RNA transcription as well as RNA degradation must take place. Accordingly, the RNA degradative machinery may adjust to the changes in RNA metabolism. Thus, a study of the response of the three major degradative exoribonucleases in Escherichia coli, polynucleotide phosphorylase, RNase II, and RNase R, to stress is of significant importance. RNase R, a processive 3' to 5' exoribonuclease, is unique among the known E. coli exoribonucleases in its ability to digest through RNAs containing extensive secondary structure without the aid of a helicase. In vivo, RNase R plays important roles in quality control of stable RNA, decay of mRNA with extensive repetitive extragenic palindromic (REP) sequences, cell-cycle regulated degradation of tmRNA in Caulobacter crescentus, as well as processing of rRNA under low temperature in P. syringae. In this dissertation, RNase R was shown to be unusual among the E. coli exoribonucleases in its dramatic response to a variety of stress conditions. Elevation of RNase R activity by as much as 10-fold was observed in response to entry into stationary phase, starvation and cold shock, and an ~3-fold increase was seen during growth in minimal medium compared to rich medium. The elevation in RNase R activity was associated with an increase in RNase R protein. Phenotypes of rnr mutants were also investigated, and RNase R was found to contribute to cell growth and viability. Further investigation of the regulation of RNase R during stress, primarily in stationary phase, revealed a novel regulation mechanism. Despite the large increase in RNase R protein and activity in stationary phase, rnr message actually decreased to only ~14% of its level in exponential phase. Further study revealed that RNase R is highly unstable in exponential phase and becomes stabilized during stationary phase, cold shock, and in minimal medium. Investigation of proteolysis on the unusual instability of RNase R indicated that both Lon and ClpXP play a role. In the absence of Lon, RNase R stability is increased ~10-fold. Based on these results, I propose that the increase in RNase R during stress is due to its enhanced stability under those conditions.
Author: David Alan Schneider
Publisher:
ISBN:
Category :
Languages : en
Pages : 248
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Author: Anne Eliane Chiaramello
Publisher:
ISBN:
Category : DNA
Languages : en
Pages : 300
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The initiation of DNA synthesis at the chromosomal replication origin, oriC, in Escherichia coli involves an RNA polymerase-mediated step. The level of synthesis of transcripts moving counterclockwise toward oriC is controlled at two promoters, P1 (asnC) and P2 (mioC), and at two transcription terminator regions, T1 and T2. As shown by S1 mapping, termination at the T2 region occurs to the right of oriC at nucleotides 297-299 and 306-310, while major termination events in the T1 region occur in and near the mioC promoter. The majority of transcripts entering oriC originates from the mioC promoter. Transcription from the mioC promoter has been shown to enhance the frequency of initiation of DNA replication of oriC containing plasmids, and to stabilize these plasmids in the host cells. The mioC promoter, which is stringently controlled, is also growth rate regulated. The amount of mioC transcripts relative to the amount of total RNA was inversely correlated with growth rate. This transcript is characterized by a short half-life (1.5 min). The mioC promoter, which contains a DnaA protein binding site, was much less susceptible to repression by DnaA protein when located in the chromosome, than when located in a plasmid. Only a very high concentration of DnaA protein repressed the mioC promoter. The DnaA protein, which is required for initiation of DNA replication from oriC, is growth rate regulated. As shown by RNase protection, this regulation is exerted at the transcriptional level, affecting both promoters, dnaAp1 and dnaAp2. Transcription from these two promoters is also stringently controlled. The amount of DnaA protein in spoT mutants, which are deficient in ppGpp pyrophosphorylase activity, decreases as the severity in the mutation increases. Thus, the intracellular concentration of ppGpp influences the expression of the dnaA gene. In conclusion, the growth rate regulation and stringent control of the dnaA gene suggest that one way in which DNA replication is coordinated with the growth rate is via ppGpp synthesis at the ribosome.
Author: E. C. C. Lin
Publisher: Springer Science & Business Media
ISBN: 1468486012
Category : Medical
Languages : en
Pages : 1010
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Book Description
This up-to-date guide focuses on the understanding of key regulatory mechanisms governing gene expression in Escherichia coli. Studies of E. coli not only provide the first models of gene regulation, but research continues to yield different control mechanisms.
Author: Ole Maaløe
Publisher:
ISBN:
Category : Bacteria
Languages : en
Pages : 306
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Author: Mingzhu Liu
Publisher:
ISBN:
Category :
Languages : en
Pages : 186
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Author: Cathleen Ann Josaitis
Publisher:
ISBN:
Category :
Languages : en
Pages : 398
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Author: Sue Jinks Robertson
Publisher:
ISBN:
Category : Proteins
Languages : en
Pages : 464
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Author: Victoria Goehner Newman
Publisher:
ISBN:
Category : DNA replication
Languages : en
Pages : 492
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Book Description
The timing of initiation of DNA replication from oriC in E. coli is regulated by the concentration of the DnaA protein. Increases in the intracellular DnaA protein concentration over 1.5 fold normal levels causes asynchronous timing of initiation of DNA replication. The regulators of the dnaA operon must keep the DnaA concentration within tight limits yet be able to respond to rapidly changing environmental conditions. Here it is shown that Fis and DnaA proteins interact, in conjunction with other factors, to regulate the expression of dnaA. Binding of DnaA to the DnaA box in the dnaA promoter region is destabilized by the binding of Fis to its binding site in dnaAp2. However, DnaA94, containing only the C-terminal 94 amino acids of the DnaA protein and retaining specific binding activity to the DnaA box of the dnaA promoter region, is not destabilized by Fis binding. DNase I and copper-phenanthroline (Cu-op) footprinting studies of DnaA and DnaA94 support the existence of a second weak DnaA box which abuts the DNase I and Cu-op footprints of Fis in the dnaAp2 promoter. We determined that the GC-rich region of the dnaAp2 promoter is analogous to the discriminator sequence (DS) of rRNA promoters, in that the GC-rich sequence mediates the repression caused by elevated levels of guanosine tetraphosphate (ppGpp). During starvation conditions, the alarmone ppGpp is synthesized. Overexpression of ppGpp causes inhibition of dnaAp2 promoter transcription, which is alleviated when the GC-rich DS is mutated to an AT-rich sequence. We conclude that this site is responsible for mediating the stringent control of the dnaAp2 promoter. Incorrect timing of initiation in the cell cycle results in asynchronous replication. Strains with a mutated DS, DnaA box, or Fis binding site in the dnaA promoter region on the chromosome have increased levels of dnaA gene expression. These mutants initiate DNA replication synchronously in minimal M9 medium as shown by flow cytometric assays. In rich medium, the DS, mutant showed very limited asynchrony, whereas the other mutants replicated synchronously.
