Atypical homeodomain protein which does not bind DNA and is required to modulate cardiac growth and development. Acts via its interaction with SRF, thereby modulating the expression of SRF-dependent cardiac-specific genes and cardiac development. Prevents SRF-dependent transcription either by inhibiting SRF binding to DNA or by recruiting histone deacetylase (HDAC) proteins that prevent transcription by SRF. Overexpression causes cardiac hypertrophy (PubMed:12297045, PubMed:12297046). Acts as a co-chaperone for HSPA1A and HSPA1B chaperone proteins and assists in chaperone-mediated protein refolding (By similarity). Interacts with serum response factor (SRF) (PubMed:12297045, PubMed:12297046). Component of a large complex containing histone deacetylases such as HDAC2 (PubMed:12975471). Interacts with the acetylated forms of HSPA1A and HSPA1B. Interacts with HSPA8 (By similarity). According to PubMed:14516659 it is cytoplasmic. Expressed in the embryonic and adult heart and in the adult brain, liver, lung, skeletal muscle, intestine and spleen. Throughout embryonic and postnatal development, it is expressed in the myocardium. First detected at 7.75 dpc in trophoblasts within extraembryonic membranes, in the lateral wings of the cardiac crescent and in the anterior head folds. At 8.0 dpc, it is expressed along the length of the linear heart tube and in the head folds. Expressed throughout the myocardium at 9.5 dpc and in the branchial arches. At 12.5 dpc, it is expressed in the heart and in the ventricular zone of the neural tube. At 13.5 dpc, it is weakly expressed in the intestinal epithelium. At 13.5 dpc and 15.5 dpc, it is also expressed in skeletal muscle, stratified epithelium (upper aerodigestive tract and skin), epithelium of developing airways, vibrissae, midbrain/hindbrain junction, meninges, mesenchymal cellular condensations that preceded cartilage formation and chondrocytes. By the transcription factor NKX2-5 that acts as a direct regulator. Mice display partial embryonic lethality and heart failure.