A PUMPKIN 72-KDA MEMBRANE-PROTEIN OF PRECURSOR-ACCUMULATING VESICLES HAS CHARACTERISTICS OF A VACUOLAR SORTING RECEPTOR

Precursor-accumulating (PAC) vesicles were previously shown to mediate the transport of the precursor of a major storage protein (pro2S albu min) to protein-storage vacuoles in developing pumpkin cotyledons. In this study, we characterized two homologous proteins from PAC vesicles , a 72 kDa protein (PV72) and an 82 kDa protein (PV82). PV72 and PV82 shouted an ability to bind to peptides derived from both an internal p ropeptide and a C-terminal peptide of pro2S albumin. PV72 was predicte d to be a type I integral membrane protein with epidermal growth facto r (EGF)-like motifs. These results suggest that PV72 and PV82 are pote ntial sorting receptors fur 2S albumin to protein-storage vacuoles.