This domain occurs at the N-terminal of Afi1, an Arf3p-interacting protein, is a protein necessary for vesicle trafficking in yeast. This domain is the interacting region of the protein which binds to Arf3, the highly conserved small GTPases (ADP-ribosylation factors). Afi1 is distributed asymmetrically at the plasma membrane and is required for polarized distribution of Arf3 but not of an Arf3 guanine nucleotide-exchange factor, Yel1p. However, Afi1 is not required for targeting of Arf3 or Yel1p to the plasma membrane. Afi1 functions as an Arf3 polarization-specific adapter and participates in development of polarity. Although Arf3 is the homologue of human Arf6 it does not function in the same way, not being necessary for endocytosis or for mating factor receptor internalization. In the S phase, however, it is concentrated at the plasma membrane of the emerging bud. Because of its polarized localisation and its critical function in the normal budding pattern of yeast, Arf3 is probably a regulator of vesicle trafficking, which is important for polarized growth.

1: Afi1p functions as an Arf3p polarization-specific docking factor for development of polarity. Tsai PC, Lee SW, Liu YW, Chu CW, Chen KY, Ho JC, Lee FJ; J Biol Chem. 2008;283:16915-16927. PMID:18397879