Evolution and Function of the RelA/SpoT Homologue (RSH) Proteins

摘要: RelA/SpoT Homologue (RSH) proteins comprise a superfamily of enzymes that synthesise and/or hydrolyse the nucleotide alarmone ppGpp, mediator ‘stringent’ response and regulator cellular metabolism in to changing environmental conditions. Most what we know about RSHs comes from Escherichia coli RelA SpoT, paralogues appear have evolved duplication an ancestral Rel gene lineage β- γ-proteobacteria. Recently, more details come light on evolution RSH superfamily, revealing there is much greater diversity than previously thought. Key Concepts: Various stress conditions (amino acid, iron fatty acid starvation, heat shock, etc.) induce so-called ‘stringent response’ bacteria chloroplasts. The stringent mediated by modulate intracellular concentration ppGpp nucleotide. ppGpp exerts its regulatory role binding modulating activity several targets: RNA polymerase, translational GTPases EF-G IF2, lysine decarboxylase Ldc1, polynucleotide phosphorylase, DnaG primase others. RelA senses amino starvation directly interacting with 70S ribosome inspecting aminoacylation status A-site tRNA, responds presence deacylated tRNA synthesising ppGpp. SpoT bifunctional enzyme has both synthetic hydrolytic activities cues net activity. Phylogenetic analyses divide protein family into 30 subgroups comprising three groups: long (such as SpoT), small synthetases (SASs) hydrolases (SAHs). In addition chloroplasts, been identified eukaryotes isolated species archaea, however ppGpp-mediated not yet these organisms. In eukaryotes, sensed general control (GAAC) system nonhomologous but functionally analogous. Keywords: RelA; SpoT; Rel; ppGpp; stringent response; ribosome; SAS; SAH; RSH; amino