title: Dependence of RelA-mediated (p)ppGpp formation on tRNA identity.
abstract: The bacterial stringent response is a cellular response to amino acid limitations and is characterized by the accumulation of the alarmone polyphosphate guanosine ((p)ppGpp). A key molecular event leading to (p)ppGpp synthesis is the binding of a deacylated tRNA to the vacant A-Site of a ribosome. The resulting ribosomal complex is recognized by and activates RelA, the (p)ppGpp synthetase. Activated RelA catalyzes (p)ppGpp formation until the deacylated tRNA passively dissociates from the ribosomal A-Site. In this report, we have investigated a novel role for the identity of A-Site bound tRNA in RelA-mediated (p)ppGpp synthesis. A comparison in the stimulation of RelA activity was made using ribosome complexes with either a tightly or weakly binding deacylated tRNA occupying the A-Site. In vitro analysis reveals that ribosome complexes formed with tight binding tRNA(Val) stimulate RelA activity at lower concentrations than that required for ribosome complexes formed with the weaker binding tRNA(Phe). The data suggest that the recovery from the stringent response may be dependent on the identity of the amino acid that was initially limiting for the bacteria.
authors.affiliation: Department of Biochemistry, School of Molecular and Systems Medicine, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
authors.forename: Roshani
authors.initials: R
authors.lastname: Payoe
authors.forename: Richard P
authors.initials: RP
authors.lastname: Fahlman
mesh_terms: D001483:Base Sequence; D002460:Cell Line; D004789:Enzyme Activation; D004926:Escherichia coli / Q000201:enzymology / Q000378:metabolism; D006158:Guanosine Pentaphosphate / Q000096:biosynthesis*; D007700:Kinetics; D008025:Ligases / Q000378:metabolism*; D012343:RNA, Transfer / Q000235:genetics / Q000378:metabolism*; D012269:Ribosomal Proteins / Q000378:metabolism
chemical_list: D012269:Ribosomal Proteins; D006158:Guanosine Pentaphosphate; C016700:ribosomal protein L7-L12; D012343:RNA, Transfer; D008025:Ligases; C028812:guanosine 3',5'-polyphosphate synthetases