title: Uni-directional growth of F-actin.
abstract: In was shown that the growth of F-actin occurs uni-directionally in vitro; that is, actin monomers (G-ADP-actin) polymerize onto only one of the two ends of a pre-existing seed in the absence of ATP. Fragments of the F-actin-heavy meromyosin complex prepared by sonication were used as seeds. By studying a large number of electron micrographs, we concluded that growth occurs on the tail end of the arrow-head structure of the seed. This result suggests that the thin filament grows in vivo from the center of the sarcomere towards the Z-line. It was further shown that the fragments of F-actin combine with both ends of the seed with nearly equal probability. These results are well interpreted according to the theory developed by Oosawa (1,2).
mesh_terms: D000199:Actins; D000244:Adenosine Diphosphate; D000818:Animals; D046911:Macromolecular Substances; D008854:Microscopy, Electron; D008956:Models, Chemical; D015879:Myosin Subfragments; D011108:Polymers; D011485:Protein Binding; D011817:Rabbits; D014783:Viscosity
chemical_list: D000199:Actins; D046911:Macromolecular Substances; D015879:Myosin Subfragments; D011108:Polymers; D000244:Adenosine Diphosphate