title: Coexpression of Escherichia coli obgE, Encoding the Evolutionarily Conserved Obg GTPase, with Ribosomal Proteins L21 and L27.
abstract: Multiple essential small GTPases are involved in the assembly of the ribosome or in the control of its activity. Among them, ObgE (CgtA) has been shown recently to act as a ribosome antiassociation factor that binds to ppGpp, a regulator whose best-known target is RNA polymerase. The present study was aimed at elucidating the expression of obgE in Escherichia coli We show that obgE is cotranscribed with ribosomal protein genes rplU and rpmA and with a gene of unknown function, yhbE We show here that about 75% of the transcripts terminate before obgE, because there is a transcriptional terminator between rpmA and yhbE As expected for ribosomal protein operons, expression was highest during exponential growth, decreased during entry into stationary phase, and became almost undetectable thereafter. Expression of the operon was derepressed in mutants lacking ppGpp or DksA. However, regulation by these factors appears to occur post-transcription initiation, since no effects of ppGpp and DksA on rplU promoter activity were observed in vitro
  
  
  
  The conserved and essential ObgE GTPase binds to the ribosome and affects its assembly. ObgE has also been reported to impact chromosome segregation, cell division, resistance to DNA damage, and, perhaps most interestingly, persister formation and antibiotic tolerance. However, it is unclear whether these effects are related to its role in ribosome formation. Despite its importance, no studies on ObgE expression have been reported. We demonstrate here that obgE is expressed from an operon encoding two ribosomal proteins, that the operon's expression varies with the growth phase, and that it is dependent on the transcription regulators ppGpp and DksA. Our results thus demonstrate that obgE expression is coupled to ribosomal gene expression.
authors.affiliation: LISM, CNRS, Aix-Marseille University, Marseille, France.
authors.forename: Rim
authors.initials: R
authors.lastname: Maouche
authors.affiliation: Department of Bacteriology, University of Wisconsin-Madison, Madison, Wisconsin, USA.
authors.forename: Hector L
authors.initials: HL
authors.lastname: Burgos
authors.affiliation: LISM, CNRS, Aix-Marseille University, Marseille, France.
authors.forename: Laetitia
authors.initials: L
authors.lastname: My
authors.affiliation: LISM, CNRS, Aix-Marseille University, Marseille, France.
authors.forename: Julie P
authors.initials: JP
authors.lastname: Viala
authors.affiliation: Department of Bacteriology, University of Wisconsin-Madison, Madison, Wisconsin, USA.
authors.forename: Richard L
authors.identifier: http://orcid.org/0000-0002-9675-5314
authors.initials: RL
authors.lastname: Gourse
authors.affiliation: LISM, CNRS, Aix-Marseille University, Marseille, France bouveret@imm.cnrs.fr.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Bouveret
mesh_terms: D001483:Base Sequence; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D009876:Operon; D010802:Phylogeny; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D029968:Escherichia coli Proteins; D012269:Ribosomal Proteins; C034661:ribosomal proteins L27; C060232:ribosomal protein L21; C491572:ObgE protein, E coli; D020559:Monomeric GTP-Binding Proteins