SNARE that acts to regulate protein transport between endosomes and the trans-Golgi network (By similarity). The SNARE complex containing STX6, STX12, VAMP4 and VTI1A mediates vesicle fusion (in vitro). Through complex formation with GRIP1, GRIA2 and NSG1 controls the intracellular fate of AMPAR and the endosomal sorting of the GRIA2 subunit toward recycling and membrane targeting (PubMed:16037816). Associates with the BLOC-1 complex. Interacts with BLOC1S6 (By similarity). Interacts with NAPA and SNAP23 (PubMed:9507000). Identified in a complex containing STX6, STX12, VAMP4 and VTI1A (PubMed:17159904). Interacts with GRIPAP1 (PubMed:20098723). Forms a complex with GRIP1, GRIA2 and NSG1; controls the intracellular fate of AMPAR and the endosomal sorting of the GRIA2 subunit toward recycling and membrane targeting (PubMed:16037816). Interacts with NSG1 (PubMed:12070131). Interacts with TPC1 (By similarity). Ubiquitous. Highly expressed in brain. Belongs to the syntaxin family.