Interacts with C-terminal domain of actin-binding protein 280. Resides in sub-nuclear structures known as SC35 speckles or nuclear splicing speckles. Isoform 1 is highly expressed in adult and fetal heart, skeletal muscle, and at a much lower levels in adipose tissue and in aorta. Undetectable in other tissues. Isoform 2 and isoform 3 are poorly detected in heart. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. Belongs to the small heat shock protein (HSP20) family.