Mediates nucleation of actin filaments and thereby promotes actin polymerization (PubMed:18403713, PubMed:26370058, PubMed:25250574, PubMed:26417072). 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 (PubMed:18403713, PubMed:26417072). Interacts (via N-terminus) with tropomyosin alpha (TPM1) (via N-terminus) (PubMed:25250574, PubMed:26873245). May also interact with TPM2 (via N-terminus) (PubMed:25250574). Colocalizes with actin filaments in sarcomeres. Detected close to the M line. Specifically expressed in heart and skeletal muscles, with higher levels in heart (at protein level). Not expressed in other tissues. Belongs to the tropomodulin family. Extended N-terminus.