May regulate gene expression and protein turnover in muscle cells. Homooligomer and heterooligomer (Probable). Interacts with titin/TTN. Interacts with myosins. Interacts with SQSTM1 and NBR1. Isoform 4 may not able to interact with isoform 1, isoform 2 and isoform 3. Probably interacts with TRIM63 and TRIM54. Nuclear under atrophic conditions and upon mechanical signals. Localizes to the sarcomeric M-band in cardiomyocytes. Colocalizes in part with microtubules (By similarity). Highly expressed in muscle. Low-level expression in liver. It is uncertain whether Met-1 or Met-17 is the initiator. Variant Arg-343 is erroneously reported as Trp-343 in PubMed:24865491.