the v-snare vamp7, and its partner t-snares: syntaxin-7, syntaxin-8, and vti1b. in yeast, the t-snares sec9p and sso2p are required for exocytosis and promote tubulovesicular budding of atg9 positive vesicles, which are also required for autophagosome biogenesis. knocking out either of these snares leads to accumulation of small atg9 containing vesicles that do not fuse, therefore preventing the formation of the pre-autophagosomal structure. in addition to phagophore assembly, snares are also important in mediating autophagosome-lysosome fusion. in mammals, the snares vamp7, vamp8, and vti1b are required in autophagosome-lysosome fusion and this process is impaired in lysosomal storage disorders where cholesterol accumulates in the lysosome and sequesters snares in cholesterol rich regions of the membrane preventing their recycling. recently, syntaxin 17 (stx17) was identified as an autophagosome associated snare that interacts with vamp8 and snap29 and is required for fusion with the lysosome. stx17 is localized on the outer membrane of autophagosomes, but not phagophores or other autophagosome precursors, which prevents them from prematurely fusing with the lysosome. in yeast, the fusion of autophagosomes with vacuoles (the yeast equivalent of lysosomes) requires snares and related proteins such as the syntaxin homolog vam3, snap-25 homolog vam7, ras-like gtpase ypt7, and the nsf ortholog, sec18. flexible substitution of components several complexes are known to flexibly substitute one protein for another: two qa-snares in yeasts can substitute for each other to some degree. yeasts which lose the r-snare - sec22p - automatically increase levels of a homolog - ykt6p - and use it the same way. although drosophilae cannot survive the loss of the snap-25 component, snap-24 can fully replace it. and also in drosophila, an r-snare not normally found in synapses can substitute for synaptobrevin. in plants snares also occur in plants and some understanding of their occurrence and role has obtained. these have often been found to be essential to vesicle transport, including zheng et al 1999's finding regarding golgi-vacuole trafficking. much of this study has been in arabidopsis.