Parcas and TRAPPII are both Rab11 GEFs and together serve an essential role in Drosophila. (A) Release of mant-GDP from 250 nM of Rab-His₆ by 50 nM of Parcas in the presence or absence of synthetic fly Golgi mix liposomes (Lipo). The Rabex domain of the Rab5 GEF Vps9 (50 nM) was used as a negative control. Traces are means. (B) Rab11 nucleotide exchange rates calculated from the plots in A. Values are means ± SEM (Parcas, n = 3; Vps9, n = 2). (C) Nucleotide exchange rates of Parcas and the Rabex domain of Vps9 on the indicated Rabs. Parcas acts on Rab11 but not Rab1 or Rab5. (D) The mean number of adult progeny with homozygous or heterozygous genotypes obtained from three independent crosses, each using five females and three males carrying the indicated mutations. The independent values are shown along with the mean. Error bars show SD. Flies were viable if they lacked Parcas or the TRAPPII subunit TRAPPC9, but not both.