Final answer:
Rab proteins are not directly involved in the SNARE mechanism of membrane fusion; they are involved in vesicle docking, whereas SNARE proteins and NSF protein participate in the fusion process itself.
Step-by-step explanation:
Among the components listed that are involved in the SNARE mechanism, the one that is NOT involved is Rab. The SNARE mechanism is crucial for the fusion of vesicles with target membranes during processes such as exocytosis and vesicular trafficking.
The key components of this mechanism include SNARE proteins (both v-SNAREs on the vesicle and t-SNAREs on the target membrane), which facilitate membrane fusion, and the NSF protein (N-ethylmaleimide sensitive factor), which disassembles SNARE complexes to allow for subsequent rounds of fusion. While Rab proteins are involved in vesicular trafficking, they primarily function in vesicle docking and not directly in the SNARE-mediated membrane fusion process.