title: Protein-nanocrystal conjugates support a single filament polymerization model in R1 plasmid segregation.
abstract: To ensure inheritance by daughter cells, many low-copy number bacterial plasmids, including the R1 drug-resistance plasmid, encode their own DNA segregation systems. The par operon of plasmid R1 directs construction of a simple spindle structure that converts free energy of polymerization of an actin-like protein, ParM, into work required to move sister plasmids to opposite poles of rod-shaped cells. The structures of individual components have been solved, but little is known about the ultrastructure of the R1 spindle. To determine the number of ParM filaments in a minimal R1 spindle, we used DNA-gold nanocrystal conjugates as mimics of the R1 plasmid. We found that each end of a single polar ParM filament binds to a single ParR/parC-gold complex, consistent with the idea that ParM filaments bind in the hollow core of the ParR/parC ring complex. Our results further suggest that multifilament spindles observed in vivo are associated with clusters of plasmids segregating as a unit.
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720, USA.
authors.forename: Charina L
authors.initials: CL
authors.lastname: Choi
authors.forename: Shelley A
authors.initials: SA
authors.lastname: Claridge
authors.forename: Ethan C
authors.initials: EC
authors.lastname: Garner
authors.forename: A Paul
authors.initials: AP
authors.lastname: Alivisatos
authors.forename: R Dyche
authors.initials: RD
authors.lastname: Mullins
mesh_terms: D000199:Actins / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism; D003102:Colloids / Q000737:chemistry; D003460:Crystallization; D004247:DNA / Q000737:chemistry; D027101:DNA Topoisomerase IV / Q000378:metabolism; D004269:DNA, Bacterial / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000378:metabolism; D006046:Gold / Q000737:chemistry; D053768:Metal Nanoparticles / Q000737:chemistry; D046529:Microscopy, Electron, Transmission; D008954:Models, Biological; D053758:Nanoparticles / Q000737:chemistry*; D010957:Plasmids / Q000378:metabolism*; D011506:Proteins / Q000737:chemistry*; D012097:Repressor Proteins / Q000378:metabolism
chemical_list: D000199:Actins; D001426:Bacterial Proteins; D003102:Colloids; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C471255:ParM protein, E coli; C086169:ParR protein, bacteria; D011506:Proteins; D012097:Repressor Proteins; D006046:Gold; D004247:DNA; D027101:DNA Topoisomerase IV