S3-12 (Adipocyte protein S3-12), also known as PLIN4 (Perilipin-4), is a 1,357 amino acid protein that belongs to the perilipin family. S3-12 contains a repeated 33–amino acid motif also found in adipophilin, and it shares protein sequence identity to both adipophilin and TIP-47 in the COOH terminus, but not to perilipin. S3-12 exhibits sequence similarity to the PAT proteins. Up-regulated during adipocyte differentiation, S3-12 may play a role in triacylglycerol packaging into adipocytes, and functions as a coat protein involved in the biogenesis of lipid storage droplets. S3-12 demonstrates highest expression in skeletal muscle, followed by heart and liver, and lowest expression in adult whole brain. Existing as two alternatively spliced isoforms, the S3-12 gene is conserved in dog, cow and mouse, and maps to human chromosome 19p13.3.