Animals have evolved mechanisms to maintain circulating nutrient levels when 
energy demands exceed feeding opportunities. Mammals store most of their energy 
as triacylglycerol in the perilipin-coated lipid droplets of adipocytes. How 
newly synthesized triacylglycerol is delivered to perilipin-coated lipid 
droplets is poorly understood. Perilipin is a member of the evolutionarily 
related family of PAT proteins (Perilipin, Adipophilin, TIP47), which is defined 
by sequence similarity and association with lipid droplets. We previously showed 
that S3-12, which is also a member of this family, associates with a separate 
pool of lipid droplets that emerge when triacylglycerol storage is driven by 
adding oleate to the culture medium of adipocytes. Our current data extend these 
findings to demonstrate that nascent lipid droplets emerge with a coat composed 
of S3-12, TIP47, and adipophilin. After 100 min of oleate treatment, the nascent 
lipid droplets are more heterogeneous: S3-12 and TIP47 coat smaller, peripheral 
droplets and adipophilin coats a more medial population of droplets. 
Fractionation of untreated and oleate-treated adipocytes shows oleate-dependent 
redistribution of TIP47 and adipophilin from cytosolic fractions to the lipid 
droplet fraction. Inhibition of protein synthesis with cycloheximide does not 
block the oleate-induced formation of the nascent lipid droplets, nor does it 
prevent TAG accumulation. We suggest that the non-lipid droplet pools of S3-12, 
adipophilin, and TIP47 constitute a ready reservoir of coat proteins to permit 
rapid packaging of newly synthesized triacylglycerol and to maximize energy 
storage during nutrient excess.