Bet3 (also known as TRAPPC3) subunit of the trafficking protein particle complex (TRAPP). Bet3 is one of the six core subunits of TRAPP complexes which play a key role in the regulation of ER-to-Golgi and intra-Golgi transport by tethering the vesicle membrane to the target membrane. TRAPPC3 has also been shown to be additionally important for membrane fusion during the formation of vesicular tubular clusters (VTC). In its core, Bet3 forms a hydrophobic channel that also contains a conserved acylation site.