cells. These types of organelles are collectively known as the cytoskeleton, and one of the most ancient systems is based on filamentous polymers of the protein actin. A polymer of a second protein, tropomyosin, is an integral part of most actin filaments in animals.

Tropomyosins are a large family of integral components of actin filaments that play a critical role in regulating the function of actin filaments in both muscle and nonmuscle cells. These proteins consist of rod-shaped coiled-coil hetero- or