Fusion between membranes is mediated by specific SNARE (soluble N-ethylmeleimide-sensitive factor attachment protein receptor) complexes. Two human SNARE proteins, VTI1A and VTI1B, are homologous to the yeast Q-SNARE Vtilp which is part of several SNARE complexes in different transport steps (PMID: 12067063). Both proteins had a distinct but overlapping localization. VTI1A is localized predominantly in the TGN, VTI1B in late endosomes (PMID:12067063; 21262811). VTI1B forms a SNARE complex with STX7, STX8 and VAMP8 which functions in the homotypic fusion of late endosomes. It is a component of the SNARE complex composed of STX7, STX8, VAMP7 and VIT1B that is required for heterotypic fusion of late endosomes with lysosomes. It has also been reported that VIT1B interacts with EpsinR, a protein involved in exocytic trafficking (PMID: 15371541).