The functions of Escherichia coli RelA and SpoT differ somewhat. RelA produces pppGpp (or ppGpp) from ATP and GTP (or GDP). SpoT degrades ppGpp, but may also act as a secondary ppGpp synthetase. The two proteins are strongly similar. In many species, a single homolog to SpoT and RelA appears reponsible for both ppGpp synthesis and ppGpp degradation. (p)ppGpp is a regulatory metabolite of the stringent response, but appears also to be involved in antibiotic biosynthesis in some species.
The functions of Escherichia coli RelA and SpoT differ somewhat. RelA (EC 2.7.6.5) produces pppGpp (or ppGpp) from ATP and GTP (or GDP). SpoT (EC 3.1.7.2) degrades ppGpp, but may also act as a secondary ppGpp synthetase. The two proteins are strongly similar. In many species, a single homologue to SpoT and RelA appears reponsible for both ppGpp synthesis and ppGpp degradation.
(p)ppGpp is a regulatory metabolite of the stringent response, but appears also to be involved in antibiotic biosynthesis in some species.
GO process:
guanosine tetraphosphate metabolic process (GO:0015969)
Family alignment:
There are 2977
RelA_SpoT domains in 2977 proteins in SMART's nrdb database.
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Evolution (species in which this domain is found)
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This tree shows only several representative species. The complete taxonomic breakdown of all proteins with RelA_SpoT domain is also avaliable.
Residual guanosine 3',5'-bispyrophosphate synthetic activity of relA nullmutants can be eliminated by spoT null mutations.
J Biol Chem. 1991; 266: 5980-90
Display abstract
It was known previously that 1) the relA gene of Escherichia coli encodesan enzyme capable of guanosine 3',5'-bispyrophosphate (ppGpp) synthesis,2) an uncharacterized source of ppGpp synthesis exists in relA nullstrains, and 3) cellular degradation of ppGpp is mainly due to amanganese-dependent ppGpp 3'-pyrophosphohydrolase encoded by the spoTgene. Here, the effects of spoT gene insertions and deletions are comparedwith analogous alterations in neighboring genes in the spo operon andfound to be lethal in relA+ strains as well as slower growing in relAlbackgrounds than delta relA hosts. Cells with null alleles in both therelA and spoT genes are found no longer to accumulate ppGpp after glucoseexhaustion or after chelation of manganese ions by picolinic acidaddition; the inability to form ppGpp is reversed by a minimal spoT geneon a multicopy plasmid. Strains apparently lacking ppGpp show a complexphenotype including auxotrophy for several amino acids and morphologicalalterations. We propose that the SpoT protein can either catalyze orcontrol the alternative pathway of ppGpp synthesis in addition to itsknown role as a (p)ppGpp 3'-pyrophosphohydrolase. We favor the possibilitythat the SpoT protein is a bifunctional enzyme capable of catalyzingeither ppGpp synthesis or degradation.
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