FIGURE 5.

The S244D mutation in rat SYT4 results in robust Ca²⁺ sensor function during reconstituted membrane fusion. A, fusion assays were carried out as described in the legend for Fig. 1B but with the indicated Syt constructs. In contrast to wild type rat SYT4, the S244D mutant stimulated membrane fusion in the presence of Ca²⁺. B, an analogous mutation was also analyzed in fly SYT4 (S284D); this mutation was largely without effect. C, the S244D mutation endowed the isolated C2A domain of SYT4 with the ability to stimulate fusion in response to Ca²⁺. Tr, t-SNARE vesicle; Vr, v-SNARE vesicle.