1

Barbed end

Barbed end

▲ EXPERIMENTAL FIGURE 19-4 Decoration demonstrates the polarity of an actin filament. Myosin S1 head domains bind to actin subunits in a particular orientation. When bound to all the subunits in a filament, S1 appears to spiral around the filament. This coating of myosin heads produces a series of arrowhead-like decorations, most easily seen at the wide views of the filament. The polarity in decoration defines a pointed (—) end and a barbed (+) end; the former corresponds to the top of the model in Figure 19-3c. [Courtesy of R. Craig.]

myosin binds to actin filaments and not to microtubules or intermediate filaments, arrowhead decoration is one criterion by which actin filaments are identified among the other cytoskeletal fibers in electron micrographs of thin-sectioned cells.

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