Figure 6. Model for Selective Targeting of Cvt Cargos into the Cvt Vesicle.
(A) Schematic drawing of binding domains in Cvt19. The prApe1 binding domain (blue) is located in the region from amino acid residues 153 to 191, which contains the predicted coiled-coil motif. The 10-amino acid region from 406 to 415 (yellow) and the 8-amino acid region from 388 to 395 (green) are for Aut7 binding and Cvt9 binding, respectively. An exact binding domain for Ams1 has not been determined but is located in a region within amino acid residues 192-387 (red arrow).
(B) After prApe1 is synthesized it immediately forms dodecamers in the cytosol, which are further assembled into an Ape1 complex dependent on its propeptide. Cvt19 then binds to the Ape1 complex, which is also mediated by the prApe1 propeptide. Because Ams1 is able to associate with Cvt19 via a domain distinct from the prApe1 binding domain, Ams1 could be concentrated on the Ape1 complex as a consequence of the Ape1-Cvt19 complex formation. Cvt9 then interacts with the C terminus of Cvt19 to recruit the Ape1-Cvt19-Ams1 complex to the PAS, where Aut7 binds to the extreme C terminus of Cvt19 to ensure the incorporation of the complex into the Cvt vesicle. See text for details.