A simplified model showing the active zone proteins involved in vesicle priming and fusion in mammals. Some of the proteins shown are RIM, Munc13, Ca2+ channels, SNAP-25, syntaxin 1, Munc18–1, complexin, Rab3 and synaptotagmin 1. Munc13 is mammalian homolog of Unc13 in nematode worm C. elegans and Dunc13 in Drosophila. Munc18 is the mammalian homolog of Unc18 in C. elegans and Drosophila.