Seipin involved in lipid droplet (LD) assembly; controls lipid particle morphology, number, and size; promotes initiation of LD formation; ensures LDs bud from the ER towards the cytosolic side of the membrane; subunit of the lipid droplet assembly complex; stabilizes ER-LD contact sites in complex with Ldb16p; regulates PA and DAG homeostasis at the inner nuclear membrane preserving envelope integrity; human homolog BSCL2 implicated in congenital lipodystrophy, complements yeast null mutant