Sattilaro, Richard F.Dentler, William L., JrLeCluyse, Edward L.2015-03-092015-03-091981-08-01Sattilaro, R. F.; Dentler, William L., Jr; LeCluyse, E. L. (1981). "Microtubule-associated proteins (MAPs) and the organization of actin filaments in vitro." Journal of Cell Biology, 90(2):467-473. http://www.dx.doi.org/10.1083/jcb.90.2.467.0021-9525https://hdl.handle.net/1808/17008This is the publisher's version, also available electronically from http://jcb.rupress.org/content/90/2/467.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.Article10.1083/jcb.90.2.467https://orcid.org/0000-0002-2149-8990openAccess