Homodimerization and heterodimerization requirements of Acinetobacter baumannii SOS response coregulators UmuDAb and DdrR revealed by two-hybrid analyses.

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From: Canadian Journal of Microbiology(Vol. 67, Issue 5)
Publisher: NRC Research Press
Document Type: Report
Length: 8,698 words
Lexile Measure: 1550L

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Abstract :

The multidrug-resistant pathogen Acinetobacter baumannii displays unusual control of its SOS mutagenesis genes, as it does not encode a LexA repressor, but instead employs the UmuDAb repressor and a small protein, DdrR, that is uniquely found in Acinetobacter species. We used bacterial adenylate cyclase two-hybrid analyses to determine if UmuDAb and DdrR coregulation might involve physical interactions. Neither quantitative nor qualitative assays showed UmuDAb interaction with DdrR. DdrR hybrid proteins, however, demonstrated modest headto-tail interactions in a qualitative assay. The similarity of UmuDAb to the homodimer-forming polymerase manager UmuD and LexA repressor proteins suggested that it may form dimers, which we observed. UmuDAb homodimerization required a free C terminus, and either small truncations or addition of a histidine tag at the C terminus abolished this homodimerization. The amino acid N100, crucial for UmuD dimer formation, was dispensable if both C termini were free to interact. However, mutation of the amino acid G124, necessary for LexA dimerization, yielded significantly less UmuDAb dimerization, even if both C termini were free. This suggests that UmuDAb forms dimers like LexA does, but may not coregulate gene expression involving a physical association with DdrR. The homodimerization of these coregulators provides insight into a LexA-independent, coregulatory process of controlling a conserved bacterial action such as the mutagenic DNA damage response. Key words: UmuDAb, LexA, DdrR, SOS response, Acinetobacter baumannii. L'agent pathogene multiresistant Acinetobacter baumannii controle de maniere inhabituelle ses genes de mutagenese SOS, car il ne code pas de represseur LexA, mais utilise plutot le represseur UmuDAb et une petite proteine, DdrR, que l'on trouve uniquement chez les especes d'Acinetobacter. Les auteurs ont utilise des analyses par double hybride de l'adenylate cyclase bacterienne pour determiner si la coregulation d'UmuDAb et de DdrR pouvait impliquer des interactions physiques. Ni les analyses quantitatives ni les analyses qualitatives n'ont montre d'interaction entre UmuDAb et DdrR. Les proteines hybrides DdrR, toutefois, montraient de modestes interactions tete-a-queue lors d'un essai qualitatif. La similarite d'UmuDAb avec le manager de polymerase UmuD et le represseur LexA qui forment des homodimeres suggere qu'il pourrait former des dimeres, ce que les auteurs ont observe. L'homodimerisation de l'UmuDAb necessitait une extremite C-terminale libre, et de petites troncatures ou l'ajout d'une etiquette d'histidine en C-terminal abolissaient cette homodimerisation. L'acide amine N100, essentiel pour la formation du dimere UmuD, n'etait pas indispensable si les deux extremites C-terminales etaient libres d'interagir. Cependant, la mutation de l'acide amine G124, necessaire a la dimerisation de LexA, entrainait une dimerisation d'UmuDAb nettement moins importante, meme si les deux extremites C-terminales etaient libres. Cela suggere qu'UmuDAb forme des dimeres comme LexA, mais ne peut pas coreguler l'expression de genes impliquant une association physique avec DdrR. L'homodimerisation de ces coregulateurs donne un apercu d'un processus de coregulation independant de LexA, permettant de controler une action bacterienne conservee telle que la reponse mutagene aux dommages a l'ADN. [Traduit par la Redaction] Mots-cles: UmuDAb, LexA, DdrR, reponse SOS, Acinetobacterbaumannii.

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Gale Document Number: GALE|A662459553