Involved in the targeting and/or fusion of transport vesicles to their target membrane during transport of proteins from the early endosome to the lysosome. Required for fusion of late endosomes with lysosomes and homotypic lysosomal fusion. May be involved in protein trafficking from the plasma membrane to the early endosome (EE) as well as in homotypic fusion of endocytic organelles. Component of the SNARE complex composed of syn7A, syn8A, vamp7A and vti1A. Interacts with nsfA, snpA and snpC. Belongs to the syntaxin family.