Regulation of the stringent response is the essential function of the conserved bacterial G protein CgtA in
            <i>Vibrio cholerae</i>

Raskin, David M.; Judson, Nicholas; Mekalanos, John J.

doi:10.1073/pnas.0611650104

Cited by 92 publications

(115 citation statements)

References 46 publications

(63 reference statements)

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“…The phenotype of the ndx8 mutant is also characterized by a wide range of transcriptional modulations observed in stringent response, e.g. down-regulation of the translational machinery (40,41) and partial activation of the ammonia assimilation (42). In addition, the current study also revealed another transcriptional The intracellular amounts of nucleotides extracted from the wild type (circle) and the ndx8 mutant (square) grown in CS medium were quantified by using HPLC.…”

Section: Discussionmentioning

confidence: 87%

Degradation of ppGpp by Nudix Pyrophosphatase Modulates the Transition of Growth Phase in the Bacterium Thermus thermophilus

Ooga

Ohashi

Kuramitsu

et al. 2009

Journal of Biological Chemistry

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A major bacterial alarmone, guanosine 3,5-bispyrophosphate (ppGpp), controls cellular growth under conditions of nutritional starvation. For most bacteria, intracellular ppGpp levels are tightly controlled by the synthesis/degradation cycle of RelA and SpoT activities. This study shows a novel ppGpp regulatory protein governing the cellular growth of Thermus thermophilus, Ndx8, a member of the Nudix pyrophosphatase family that degrades ppGpp to yield guanosine 3,5-bisphosphate. The ndx8-null mutant strain exhibited early stage growth arrest accompanied by the stationary phase-specific morphologies and global transcriptional modulation under nutritionally defined conditions. Several possible substrate compounds of Ndx8, which specifically accumulated in the ndx8 mutant cells, were identified by employing a capillary electrophoresis time-of-flight mass spectrometry-based metabolomics approach. Among them, the hydrolytic activity of Ndx8 for ppGpp was significant not only in vitro but also in vivo. Finally, the elimination of ppGpp synthetic activity suppressed the observed phenotype of the ndx8 mutation, suggesting that the function of Ndx8 as a growth regulator is involved in ppGpp accumulation, which is thought to act as a trigger of the growth phase transition. These results suggest a novel mechanism of ppGpp-mediated growth control by the functional relay between Ndx8 and SpoT activity as ppGpp scavengers.The stringent response, which is a pleiotropic adaptation to nutritional starvation and stress, is broadly conserved in bacteria and plant chloroplasts (1, 2). This physiological control is dominated by a rapid synthesis/degradation cycle of the stringent alarmones guanosine 3Ј-pyrophosphate 5Ј-triphosphate (pppGpp) 4 or guanosine 3Ј,5Ј-bispyrophosphate (ppGpp) ( Fig. 1) (3). In Escherichia coli grown under amino acid depletion, pppGpp is synthesized from ATP and GTP by ribosome-associated RelA activity and subsequently converted to ppGpp by the activity of 5Ј-nucleotidase (4). Besides this pathway, ppGpp is also directly synthesized from GDP by the activity of RelA. Thereafter, ppGpp is degraded to GDP and pyrophosphate by the activity of SpoT, which is a RelA homolog with reciprocal activities for ppGpp degradation and synthesis (5, 6). For several bacteria, SpoT physiologically acts as both the ppGpp synthetase and hydrolase and is known as the Rel/Spo homolog. The metabolism of these alarmone nucleotides is understood based on the function of these two enzymes, whereas recent studies have identified alternative players acting as ppGpp synthetase in bacteria (7,8). On the other hand, for the degradation of ppGpp, previous studies reported that SpoT-independent (p)ppGpp degradation activity exists in bacteria, whereas the biological meaning(s) and enzymatic mechanism(s) of these alternative pathways have not been characterized in any organisms (9 -12).The Nudix hydrolases constitute a large family of proteins that share a highly conserved amino acid sequence, the so-called "Nudix motif," which is distribut...

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Section: Discussionmentioning

confidence: 87%

Degradation of ppGpp by Nudix Pyrophosphatase Modulates the Transition of Growth Phase in the Bacterium Thermus thermophilus

Ooga

Ohashi

Kuramitsu

et al. 2009

Journal of Biological Chemistry

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“…The defect occurred at both the permissive and restrictive temperatures, suggesting that this is not the essential function of Obg (Datta et al, 2004). Recent studies show that Vibrio cholera Obg is dispensable in a relA deletion mutant and essentially acts as a repressor of the stringent response by regulating SpoT activity to maintain low ppGpp levels when bacteria grow in nutrient-rich conditions (Raskin et al, 2007). B. subtilis yqeH is classified as an essential gene due to the inability of the IPTG-dependent P spac -yqeH mutant to grow on LB or PAB agar plates in the absence of IPTG.…”

Section: Discussionmentioning

confidence: 99%

The GTP-binding protein YqeH participates in biogenesis of the 30S ribosome subunit in Bacillus subtilis

et al. 2007

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Bacterial genome sequencing has revealed a novel family of P-loop GTPases that are often essential for growth. Accumulating evidence suggests that these proteins are involved in biogenesis of the 30S or 50S ribosomal subunits. YqeH is a member of this Obg/Era GTPase family, with its function remains to be uncovered. Here, we present results showing that YqeH is involved in the 30S subunit biogenesis in Bacillus subtilis. We observed a reduction in the 70S ribosome and accumulation of the free 50S subunit in YqeH-depleted cells. Interestingly, no free 30S subunit accumulation was evident. Consistent with the theory that YqeH is involved in 30S subunit biogenesis, a precursor of 16S rRNA and its degradation products were detected. Additionally, the reduction of free 30S subunit was not observed in Eradepleted cells. YqeH overexpression did not compensate for growth defects in mutants devoid of Era and vice versa. Moreover, in vitro GTPase analyses showed that YqeH possessed high intrinsic GTPase activity. In contrast, Era showed slow GTPase activity, which was enhanced by the 30S ribosomal subunit. Our findings strongly suggest that YqeH and Era function at distinct checkpoints during 30S subunit assembly. B. subtilis yqeH is classified as an essential gene due to the inability of the IPTG-dependent P spac -yqeH mutant to grow on LB or PAB agar plates in the absence of IPTG. However, in our experiments, the P spac -yqeH mutant grew in PAB liquid medium without IPTG supplementation, albeit at an impaired rate. This finding raises the interesting possibility that YqeH participates in assembly of the 30S ribosomal subunit as well as other cellular functions essential for growth on solid media.

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“…Recent results in Vibrio cholerae (Raskin et al, 2007) suggest that the Obg orthologue, CgtA, is required to downregulate the stringent response, perhaps by modulation of the ppGpp hydrolase activity of SpoT. Cells depleted for CgtA show gene expression patterns characteristic of constitutive induction of the stringent response.…”

Section: Obg and The Stringent Responsementioning

confidence: 99%

Chromosome segregation control by Escherichia coli ObgE GTPase

Foti

Persky²,

Ferullo

et al. 2007

Molecular Microbiology

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SummaryEscherichia coli cells depleted of the conserved GTPase, ObgE, show early chromosome-partitioning defects and accumulate replicated chromosomes in which the terminus regions are colocalized. Cells lacking ObgE continue to initiate replication, with a normal ratio of the origin to terminus. Localization of the SeqA DNA binding protein, normally seen as punctate foci, however, was disturbed. Depletion of ObgE also results in cell filamentation, with polyploid DNA content. Depletion of ObgE did not cause lethality, and cells recovered fully after expression of ObgE was restored. We propose a model in which ObgE is required to license chromosome segregation and subsequent cell cycle events.

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Regulation of the stringent response is the essential function of the conserved bacterial G protein CgtA in Vibrio cholerae

Cited by 92 publications

References 46 publications

Degradation of ppGpp by Nudix Pyrophosphatase Modulates the Transition of Growth Phase in the Bacterium Thermus thermophilus

Degradation of ppGpp by Nudix Pyrophosphatase Modulates the Transition of Growth Phase in the Bacterium Thermus thermophilus

The GTP-binding protein YqeH participates in biogenesis of the 30S ribosome subunit in Bacillus subtilis

Chromosome segregation control by Escherichia coli ObgE GTPase

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