Mediates nucleation of actin filaments and thereby promotes actin polymerization (PubMed:18403713). Plays a role in the regulation of actin filament length (By similarity). Required for normal sarcomere organization in the heart, and for normal heart function (PubMed:18403713). Can bind at least three actin monomers and thereby provides a nucleus for actin filament formation. Interacts (via N-terminus) with tropomyosin alpha (TPM1) (via N-terminus). May also interact with TPM2 (via N-terminus). Colocalizes with actin filaments in sarcomeres. Detected close to the M line. Belongs to the tropomodulin family.