The function of ENSG00000136305 (CIDEB, cell death inducing DFFA like effector b) is as follows. Lipid transferase specifically expressed in hepatocytes, which promotes unilocular lipid droplet formation by mediating lipid droplet fusion (PubMed:35939579). Lipid droplet fusion promotes their enlargement, restricting lipolysis and favoring lipid storage (PubMed:35939579). Localizes on the lipid droplet surface, at focal contact sites between lipid droplets, and mediates atypical lipid droplet fusion by promoting directional net neutral lipid transfer from the smaller to larger lipid droplets (By similarity). The transfer direction may be driven by the internal pressure difference between the contacting lipid droplet pair (By similarity). Promotes lipid exchange and lipid droplet fusion in both small and large lipid droplet- containing hepatocytes (By similarity). In addition to its role in lipid droplet fusion, also involved in cytoplasmic vesicle biogenesis and transport (By similarity). Required for very-low-density lipoprotein (VLDL) lipidation and maturation (By similarity). Probably involved in the biogenesis of VLDL transport vesicles by forming a COPII vesicle coat and facilitating the formation of endoplasmic reticulum-derived large vesicles (By similarity). Also involved in sterol-regulated export of the SCAP-SREBP complex, composed of SCAP, SREBF1/SREBP1 and SREBF2/SREBP2, by promoting loading of SCAP-SREBP into COPII vesicles (By similarity). May also activate apoptosis (PubMed:10619428). {ECO:0000250|UniProtKB:O70303, ECO:0000250|UniProtKB:P56198, ECO:0000269|PubMed:10619428, ECO:0000269|PubMed:35939579}. (Microbial infection) Involved in Hepatatis C virus (HCV) assembly and required for HCV entry into hepatocytes. .