RelA/SpoT protein <p>The functions of <taxon tax_id="562">Escherichia coli</taxon> RelA and SpoT differ somewhat. RelA (<db_xref db="EC" dbkey="2.7.6.5"/>) produces pppGpp (or ppGpp) from ATP and GTP (or GDP). SpoT (<db_xref db="EC" dbkey="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 responsible for both ppGpp synthesis and ppGpp degradation. </p> <p> (p)ppGpp is a regulatory metabolite of the stringent response, but appears also to be involved in antibiotic biosynthesis in some species. </p>