title: Molecular handcuffing of the relaxosome at the origin of conjugative transfer of the plasmid R1162.
abstract: The assembly of plasmid-encoded proteins at a unique site (oriT) on the plasmid R1162, to form a complex called the relaxosome, is required for conjugative transfer of the plasmid and for negative regulation of neighboring promoters. Two-dimensional chloroquine gel electrophoresis was used to show that oriTs are physically coupled at the relaxosome. This interaction requires all the relaxosome proteins, which are assembled into a structure resulting in a decrease in the average linking number of the plasmid DNA in the cell. Molecules with higher superhelical densities are preferentially selected for assembly of the relaxosome. Genetic data obtained earlier indicate that the molecular coupling reported here is a 'handcuffing' reaction that contributes to the regulation of adjacent plasmid promoters. However, although these promoters affect the expression of the genes for replication, plasmid copy-control is regulated independently. This is the first time 'handcuffing' has been observed at an oriT, and its possible significance for transfer is discussed.
authors.affiliation: Section of Molecular Genetics and Microbiology and The Institute for Molecular Biology, School of Biology, University of Texas at Austin, Austin, TX 78712, USA.
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Zhang
authors.forename: Shuyu
authors.initials: S
authors.lastname: Zhang
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Meyer
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D003227:Conjugation, Genetic / Q000235:genetics*; D019281:Dimerization; D004926:Escherichia coli / Q000235:genetics; D009154:Mutation; D010957:Plasmids / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D011485:Protein Binding
chemical_list: D001426:Bacterial Proteins