title: Microtubule-associated proteins (MAPs) and the organization of actin filaments in vitro.
abstract: When purified muscle actin was mixed with microtubule-associated proteins (MAPs) prepared from brain microtubules assembled in vitro, actin filaments were organized into discrete bundles, 26 nm in diameter. MAP-2 was the principal protein necessary for the formation of the bundles. Analysis of MAP-actin bundle formation by sedimentation and electrophoresis revealed the bundles to be composed of approximately 20% MAP-2 and 80% actin by weight. Transverse striations were observed to occur at 28-nm intervals along negatively stained MAP-actin bundles, and short projections, approximately 12 nm long and spaced at 28-nm intervals, were resolved by high-resolution metal shadowing. The formation of MAP-actin bundles was inhibited by millimolar concentrations of ATP, AMP-PCP (beta, gamma-methylene-adenosine triphosphate), and pyrophosphate but not by AMP, ADP, or GTP. The addition of ATP to a solution containing MAP-actin bundles resulted in the dissociation of the bundles into individual actin filaments; discrete particles, presumably MAP-2, were periodically attached along the splayed filaments. These results demonstrate that MAPs can bind to actin filaments and can induce the reversible formation of actin filament bundles in vitro.
mesh_terms: D000199:Actins / Q000032:analysis; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000249:Adenosine Monophosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D003599:Cytoskeleton / Q000648:ultrastructure*; D011756:Diphosphates / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D046911:Macromolecular Substances; D008869:Microtubule-Associated Proteins; D011506:Proteins / Q000032:analysis
chemical_list: D000199:Actins; D011756:Diphosphates; D046911:Macromolecular Substances; D008869:Microtubule-Associated Proteins; D011506:Proteins; C005147:5'-adenylyl (beta,gamma-methylene)diphosphonate; D000249:Adenosine Monophosphate; D000244:Adenosine Diphosphate; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; C002630:alpha,beta-methyleneadenosine 5'-triphosphate