text: The proteins CDC42 and Rac1 stimulate the formation of structures composed of this protein.
full_question: The proteins CDC42 and Rac1 stimulate the formation of structures composed of this protein. Staining of structures containing this protein is typically done with phalloidin derivatives. Lengthening of structures made of this protein is promoted by formin, while its branching is caused by the Arp2/3 complex. This protein's "barbed end," where polymerization typically occurs, can bind to the protein CapZ, which prevents assembly. This protein's binding sites are blocked by tropomyosin bound to the troponin complex within the sarcomere. For 10 points name this protein which is bound to by myosin during muscle contraction, and which makes up the microfilaments of the cytoskeleton.
first_sentence: The proteins CDC42 and Rac1 stimulate the formation of structures composed of this protein.
raw_answer: actin