Thin filament-associated protein that is implicated in actin bundling and actin filament dynamics (PubMed:7929573, PubMed:7929572, PubMed:11096113, PubMed:17684058, PubMed:25717181). Exhibits F-actin cross-linking activity (PubMed:11096113, PubMed:17684058). Required for the maintenance of sarcomeric actin organization in striated muscles (PubMed:7929573, PubMed:7929572). Competes with unc-60 isoform b for actin binding and protects actin filaments from depolymerization by unc-60, thereby contributing to actin filament stability (PubMed:17684058). Cooperates with myosin to form actomyosin bundles and inhibits actomyosin ATPase activity and actomyosin motility (PubMed:25717181). Might protect the myofilaments from mechanical stress (PubMed:7929572). Acts as a negative regulator of myosin-dependent contractility of smooth muscle-like cells in the somatic gonad. Monomer (PubMed:11096113). Interacts with F-actin (PubMed:11096113, PubMed:25717181). Interacts with myosin (PubMed:25717181). Absent from the distal edges of the thin filament. Isoform b: Partially overlaps with the region where myo-3 is located. Expressed in the body wall muscles (PubMed:17684058). Isoform a: Expression in the pharynx, anal depressor muscle, uterine muscle, vulva and unidentified neurons in the head and the ventral region (PubMed:25717181). Isoform b: Expression in the body wall muscles, spermatheca, vulva and in the myoepithelial sheath (PubMed:25717181). Calponin-like repeats 1-3 are required for actin binding and acting bundling activity. Defects in the structure and function of body wall muscle, resulting in variable paralysis (PubMed:7929573). Disorganization of the A- and I-bands of the myofilament lattice and accumulation of thin filaments in body wall muscles in adult animals (PubMed:7929572). More densely aligned myosin filaments indicating higher contractility of the actomyosin network (PubMed:25717181). Excessive contraction of the myoepithelial sheath (PubMed:25717181). Belongs to the calponin family.