Disease relevance of relA

• The global transcriptional regulator (p)ppGpp (guanosine-3'-diphosphate-5'-triphosphate and guanosine-3',5'-bisphosphate, collectively) produced by the relA and spoT genes in Escherichia coli allows bacteria to adapt to different environmental stresses [1].
• Moreover, the wild-type allele of Myxococcus relA rescues DK527 [2].
• In order to evaluate the role of the stringent response in starvation adaptations of the marine Vibrio sp. strain S14, we have cloned the relA gene and generated relaxed mutants of this organism [3].
• Characterization of the relA gene of Porphyromonas gingivalis [4].
• The autolysis mechanisms in amino acid-deprived relA mutant cells treated with chloramphenicol were temperature sensitive [5].

High impact information on relA

• We find that rRNA synthesized from plasmids does exhibit a relA-dependent, stringent response [6].
• Cyclic AMP can replace the relA-dependent requirement for derepression of acetohydroxy acid synthase in E. coli K-12 [7].
• Mutations in a nonessential viral gene permit bacteriophage T4 to form plaques on Escherichia coli valS ts relA [8].
• Ectopic increase in the intracellular concentration of (p)ppGpp was achieved in M. xanthus by introducing a copy of the E. coli relA gene, whose product catalyzes pyrophosphate transfer from ATP- to GTP-forming pppGpp [9].
• Many of these changes depend on the regulatory nucleotide ppGpp (guanosine tetraphosphate) synthesized by RelA (ppGpp synthetase I), the relA-encoded protein [10].

Chemical compound and disease context of relA

• Addition of divalent ion chelating agents picolinic acid, 1,10-phenanthroline, or quinoline-2-carboxylic acid to wild type, relA, or relX, but not spoT strains of Escherichia coli increases the levels of guanosine 5'-diphosphate 3'-diphosphate (ppGpp) [11].
• The relA mutation did not affect long-term survival or the development of resistance against heat, ethanol, and oxidative stress during carbon starvation of Vibrio sp. strain S14 [3].
• These findings indicate that 4-thiouridine is almost the sole chromophore for this effect in E. coli B/r, but that only 50% of the effect operates by a mechanism utilizing the relA(+) gene product; growth delay appears not to be primarily involved [12].
• The relA gene is not required for glycogen accumulation during NH4+ starvation of Escherichia coli [13].
• In this study, we demonstrate that overexpression of the relA gene, encoding ppGpp synthetase, increases the accumulation of amino acids, such as glutamate and lysine, in amino-acid-overproducing strains of E. coli [14].

Biological context of relA

• The genome of Borrelia burgdorferi encodes a single chromosomal rel gene (BB0198) (B. burgdorferi rel [rel(Bbu)]) homologous to relA and spoT of E. coli [1].
• Induction of a relA gene deletion mutant in pSM11 containing 455 amino-terminal amino acids results in much lower levels of expression of a metabolically unstable 55-kDa protein and elevated ppGpp levels that are almost equivalent to induced pSM10 and are relC-independent [15].
• It is also demonstrated that relA knock-outs diminish the high persistent phenotype in hipA7 mutants and that relA spoT knock-outs eliminate high persistence altogether, suggesting that hipA7 facilitates the establishment of the persister state by inducing (p)ppGpp synthesis [16].
• We have previously reported that mazEF, the first regulatable chromosomal 'addiction module' located on the Escherichia coli chromosome, downstream from the relA gene, plays a crucial role in the programmed cell death in bacteria under stressful conditions [17].
• Mutation in the relA gene of Vibrio cholerae affects in vitro and in vivo expression of virulence factors [18].

Anatomical context of relA

• In amino acid-rich media, isopropyl-1-thio-beta-D-galactopyranoside induction of transcription of the wild type relA gene in pSM10 yields about a 100-fold overexpression of a metabolically stable, full length (743 amino acid) RelA protein to levels approximating the number of cellular ribosomes [15].
• Studies of stringent controlled Escherichia coli CP78 (relA+) and relaxed controlled E. coli CP79 (relA-) were carried out to test whether these strains differ in the appearance of their cytoplasmic membranes after induction of stringent and relaxed response [19].
• The effects of amino acid starvation on the metabolic behavior of polysomes and the size distribution of proteins have been studied in an otherwise isogenic pair of stringent (relA+) and relaxed (relA) strains of Escherichia coli [20].

Associations of relA with chemical compounds

• Intracellular levels of guanosine 3',5'-bispyrophosphate (ppGpp) governed by the relA gene are normally regulated by aminoacyl-tRNA availability for protein synthesis [15].
• This results in a slow but significant accumulation of this regulatory nucleotide in a relA mutant during serine starvation [21].
• Both relA1 and relA null strains accumulate ppGpp during glucose starvation and do not accumulate ppGpp during the stringent response [22].
• The most widely studied "relaxed" mutant of the relA locus, the relA1 allele, is shown here to consist of an IS2 insertion between the 85th and 86th codons of the otherwise wild-type relA structural gene, which normally encodes a 743-amino acid (84 kDa) protein [22].
• Nutrient starvation experiments and the use of relA spoT mutant strains, IPTG-regulated overproduction of ppGpp and lacZ fusions revealed that the stringent response alarmone guanosine 3',5'-bispyrophosphate (ppGpp) is the main positive effector of Cka synthesis [23].

Regulatory relationships of relA

• We found that overexpression of relA activated the expression of rpoS in P. aeruginosa and led to premature, cell density-independent LasB elastase production [24].
• Interestingly, the cfa promoter expression is repressed in a L. lactis relA* mutant which accumulates (p)ppGpp, whereas its induction by acidity appeared independent of (p)ppGpp in L. lactis and in Escherichia coli [25].

Other interactions of relA

• The activation was dependent on relA and spoT, which encode enzymes for the synthesis and degradation of ppGpp, and on dksA, which encodes an RNA polymerase accessory protein required for the stringent response [26].

Analytical, diagnostic and therapeutic context of relA

• Northern blot and reverse transcriptase PCR analyses indicated significant reduction in the transcript levels of both virulence factors in the relA mutant strain SHK17 [18].
• Stringent control during carbon starvation of marine Vibrio sp. strain S14: molecular cloning, nucleotide sequence, and deletion of the relA gene [3].
• Deletion of the relA gene generated a (p)ppGpp0 phenotype that demonstrated its essential role in the response to amino acid deprivation and resulted in impaired/lowered induction of proteins involved in stress response as well as amino acid biosynthesis, as judged by two-dimensional gel electrophoresis [27].
• Scanning confocal laser microscopy demonstrated the cell densities of microcolonies in the relA spoT mutant to be lower than those in the wild type [28].
• The combination of the chromosomal relA mutation and a conditional suicide system of this type provides an effective means of biological containment for recombinant E. coli strains [29].

References