title: Interaction of microtubule-associated proteins with actin filaments. Studies using the fluorescence-photobleaching recovery technique.
abstract: The interaction of microtubule-associated proteins with actin filaments has been investigated by measuring the diffusion coefficient of either the filament or the microtubule-associated proteins. Experiments were performed using the technique of fluorescence photobleaching recovery with actin labeled with iodoacetamidotetramethyl rhodamine or microtubule-associated proteins labeled with iodoacetamidofluorescein. Actin filaments composed of pure rhodamine-labeled actin are not immobilized under a variety of conditions (Tait, J. F., and Frieden, C. (1982c) Biochemistry 21, 6046-6053). We find that addition of microtubule-associated proteins to rhodamine-labeled actin in a ratio as low as 1:1000 can cause immobilization, presumably cross-linking actin into a network of nondiffusible filaments. Immobilization occurs after polymerization is complete, suggesting either a length redistribution of actin filaments, a redistribution of the cross-links between filaments, or the slow addition of actin filaments to other filaments via the microtubule-associated protein. Experiments using fluorescein-labeled microtubule-associated proteins show that these proteins are bound to actin filaments as they are formed and that binding depended on actin concentration, indicating that there are a number of binding sites on the actin filaments. However, while the actin filaments become completely immobilized, the microtubule-associated proteins become only partially immobilized suggesting at least two different classes of binding affinities. The large peptide obtained from trypsin-treated fluorescein-labeled microtubule-associated proteins is not able to immobilize actin filaments since it does not bind to the filaments.
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D001923:Brain Chemistry; D002417:Cattle; D005453:Fluorescence; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D010777:Photochemistry; D011108:Polymers / Q000378:metabolism; D012235:Rhodamines / Q000378:metabolism; D013997:Time Factors; D014357:Trypsin / Q000378:metabolism
chemical_list: D000199:Actins; D008869:Microtubule-Associated Proteins; D011108:Polymers; D012235:Rhodamines; D014357:Trypsin