title: Penicillin binding protein 2 is dispensable in Escherichia coli when ppGpp synthesis is induced.
abstract: Mecillinam, a beta-lactam antibiotic which specifically inactivates penicillin binding protein 2 (PBP2) in Escherichia coli, prevents lateral cell wall elongation, inducing spherical morphology and cell death. Two mecillinam resistant mutants, lov-1 and lovB, both able to dispense entirely with PBP2, are shown here to be affected in the aminoacyl-tRNA synthetase genes argS and alaS, respectively. Although the argS and alaS mutants grow slowly, we show that there is no correlation between mecillinam resistance and either growth rate or translation speed. A role of the ribosomes in mecillinam sensitivity, suggested by our earlier report that the lov-1 mutation is suppressed by certain rpsL(StrR) alleles affecting ribosomal protein S12, is supported by the present observation that a pseudo-streptomycin dependent mutant is mecillinam resistant in the presence of streptomycin. The argS and alaS mutants have high pools of the nucleotide ppGpp (effector of the stringent response) and the mecillinam resistance of both mutations is suppressed by a relA mutation, inactivating the ribosome-associated ppGpp synthetase and preventing ppGpp synthesis in response to aminoacyl-tRNA starvation. Furthermore, a ptacrelA' multicopy plasmid makes a wild type strain mecillinam resistant. The effect of ppGpp is probably mediated by RNA polymerase, since sublethal doses of the polymerase inhibitor rifampicin suppress mecillinam resistance in argS, alaS and ptacrelA'-bearing strains. We conclude that ppGpp regulates the transcription of a gene whose product is involved in mecillinam sensitivity, possibly as part of a chain of interacting elements which coordinate ribosomal activity with that of the PBPs.
authors.affiliation: Institut Jacques Monod, Université Paris 7, France.
authors.forename: D
authors.initials: D
authors.lastname: Vinella
authors.forename: R
authors.initials: R
authors.lastname: D'Ari
authors.forename: A
authors.initials: A
authors.lastname: Jaffé
authors.forename: P
authors.initials: P
authors.lastname: Bouloc
mesh_terms: D000412:Alanine-tRNA Ligase / Q000235:genetics; D000483:Alleles; D000560:Amdinocillin / Q000494:pharmacology; D001126:Arginine-tRNA Ligase / Q000235:genetics; D001426:Bacterial Proteins; D002352:Carrier Proteins; D002455:Cell Division; D002874:Chromosome Mapping; D004352:Drug Resistance, Microbial / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D005838:Genotype; D006159:Guanosine Tetraphosphate / Q000096:biosynthesis / Q000378:metabolism*; D006602:Hexosyltransferases / Q000235:genetics / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism*; D002267:Muramoylpentapeptide Carboxypeptidase; D009154:Mutation; D046915:Penicillin-Binding Proteins; D010458:Peptidyl Transferases / Q000235:genetics / Q000378:metabolism*; D015183:Restriction Mapping; D000091243:Ribosomal Protein S9; D012270:Ribosomes / Q000378:metabolism; D012293:Rifampin / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D009097:Multienzyme Complexes; D046915:Penicillin-Binding Proteins; D000091243:Ribosomal Protein S9; C000717190:RpsI protein, E coli; D006159:Guanosine Tetraphosphate; D010458:Peptidyl Transferases; D006602:Hexosyltransferases; D002267:Muramoylpentapeptide Carboxypeptidase; D001126:Arginine-tRNA Ligase; D000412:Alanine-tRNA Ligase; D000560:Amdinocillin; D012293:Rifampin