title: Kid, a small protein of the parD stability system of plasmid R1, is an inhibitor of DNA replication acting at the initiation of DNA synthesis.
abstract: The Kid and Kis proteins are the killer component and the antagonist belonging to parD, a killer stability system of plasmid R1. The Kid and Kis proteins have been purified, the second one as a C-LYT-Kis fusion that conserves the antagonistic activity of the Kis protein, but not its auto-regulatory potential. Kid inhibits in vitro replication of CoEl to a basal level without altering the superhelicity of the template but it does not substantially affect in vitro replication of P4, a DnaA, DnaB, DnaC and DnaG-independent replicon. Kid inhibits lytic induction of a lambda, prophage, but this inhibition can be neutralized by excess DnaB. In addition, a multicopy dnaB recombinant, but not a multicopy dnaG recombinant, prevents the toxicity associated with this protein. Inhibition of ColE1 replication by Kid in vitro is prevented by the C-LYT-Kis protein. Functional analysis indicates that the antagonistic activity of Kis is independent of its activity as a co-regulator of the parD promoter. It is also shown that C-LYT-Kis and Kid interact, forming a tight complex. These results strongly suggest that the toxicity of the kid protein is due to inhibition of DnaB-dependent DNA replication, and that direct protein-protein interactions are involved in the neutralization of the activity of the killer protein by the antagonist.
authors.affiliation: Centro de Investigaciones Biológicas, C.S.I.C. Velázquez, Madrid, Spain.
authors.forename: M J
authors.initials: MJ
authors.lastname: Ruiz-Echevarría
authors.forename: G
authors.initials: G
authors.lastname: Giménez-Gallego
authors.forename: R
authors.initials: R
authors.lastname: Sabariegos-Jareño
authors.forename: R
authors.initials: R
authors.lastname: Díaz-Orejas
mesh_terms: D001426:Bacterial Proteins / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*; D004261:DNA Replication / Q000187:drug effects*; D004268:DNA-Binding Proteins; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins; D010957:Plasmids
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C489746:ParD protein, E coli; C489749:ParD protein, Plasmid R1; C078613:parD protein, Bacteria