title: ComE/ComE~P interplay dictates activation or extinction status of pneumococcal X-state (competence).
abstract: Since 1996, induction of competence for genetic transformation of Streptococcus pneumoniae is known to be controlled by the ComD/ComE two-component regulatory system. The mechanism of induction is generally described as involving ComD autophosphorylation, transphosphorylation of ComE and transcriptional activation by ComE~P of the early competence (com) genes, including comX which encodes the competence-specific σ(X) . However, none of these features has been experimentally established. Here we document the autokinase activity of ComD proteins in vitro, and provide an estimate of the stoichiometry of ComD and ComE in vivo. We report that a phosphorylmimetic mutant, ComE(D58E), constructed because of the failure to detect transphosphorylation of purified ComE in vitro, displays full spontaneous competence in ΔcomD cells, an that in vitro ComE(D58E) exhibits significantly improved binding affinity for P(comCDE). We also provide evidence for a differential transcriptional activation and repression of P(comCDE) and P(comX). Altogether, these data support the model of ComE~P-dependent activation of transcription. Finally, we establish that ComE antagonizes expression of the early com genes and propose that the rapid deceleration of transcription from P(comCDE) observed even in cells lacking σ(X) is due to the progressive accumulation of ComE, which outcompetes ComE~P.
authors.affiliation: Centre National de la Recherche Scientifique, LMGM-UMR5100, F-31000 Toulouse, France.
authors.forename: Bernard
authors.initials: B
authors.lastname: Martin
authors.forename: Anne-Lise
authors.initials: AL
authors.lastname: Soulet
authors.forename: Nicolas
authors.initials: N
authors.lastname: Mirouze
authors.forename: Marc
authors.initials: M
authors.lastname: Prudhomme
authors.forename: Isabelle
authors.initials: I
authors.lastname: Mortier-Barrière
authors.forename: Chantal
authors.initials: C
authors.lastname: Granadel
authors.forename: Marie-Françoise
authors.initials: MF
authors.lastname: Noirot-Gros
authors.forename: Philippe
authors.initials: P
authors.lastname: Noirot
authors.forename: Patrice
authors.initials: P
authors.lastname: Polard
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Claverys
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D061269:DNA Transformation Competence; D015964:Gene Expression Regulation, Bacterial; D008954:Models, Biological; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D025941:Protein Interaction Mapping; D013296:Streptococcus pneumoniae / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; C103179:ComE protein, Streptococcus pneumoniae