Caldesmon is a potential actomyosin regulatory protein found in smooth muscle and nonmuscle cells. The predicted smooth-muscle polypeptide is 793 amino acids long. The high molecular weight caldesmon (h-CaD) is predominantly expressed in smooth muscles, whereas the low molecular weight caldesmon (l-CaD) is widely distributed in nonmuscle tissues and cells. Hayashi et al. (1992) demonstrated that the human CDM gene is composed of 14 exons.