title: Concerning the dynamic instability of actin homolog ParM.
abstract: Using in vitro TIRF- and electron-microscopy, we reinvestigated the dynamics of native ParM, a prokaryotic DNA segregation protein and actin homolog. In contrast to a previous study, which used a cysteine ParM mutant, we find that the polymerization process of wild type ATP-ParM filaments consists of a polymerization phase and a subsequent steady state phase, which is dynamically unstable, like that of microtubules. We find that the apparent bidirectional polymerization of ParM, is not due to the intrinsic nature of this filament, but results from ParM forming randomly oriented bundles in the presence of crowding agents. Our results imply, that in the bacterium, ParM filaments spontaneously form bipolar bundles. Due to their intrinsic dynamic instability, ParM bundles can efficiently "search" the cytoplasmic lumen for DNA, bind it equally well at the bipolar ends and segregate it approximately symmetrically, by the insertion of ParM subunits at either end.
authors.affiliation: ERATO Actin Filament Dynamics Project, Japan Science and Technology Corporation, c/o RIKEN Harima Institute at Spring 8, Kouto, Sayo, Hyogo 679-5148, Japan. dpopp@spring8.or.jp
authors.forename: David
authors.initials: D
authors.lastname: Popp
authors.forename: Akihiro
authors.initials: A
authors.lastname: Yamamoto
authors.forename: Mitsusada
authors.initials: M
authors.lastname: Iwasa
authors.forename: Akihiro
authors.initials: A
authors.lastname: Narita
authors.forename: Kayo
authors.initials: K
authors.lastname: Maeda
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Maéda
mesh_terms: D000199:Actins / Q000737:chemistry* / Q000648:ultrastructure*; D016880:Anisotropy; D019281:Dimerization; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D007700:Kinetics; D046912:Multiprotein Complexes / Q000737:chemistry / Q000648:ultrastructure; D010316:Particle Size; D011487:Protein Conformation
chemical_list: D000199:Actins; D029968:Escherichia coli Proteins; D046912:Multiprotein Complexes; C471255:ParM protein, E coli