The sorting of the yeast proteases proteinase A and carboxypeptidase Y
to the vacuole is a saturable, receptor-mediated process. Information
sufficient for vacuolar sorting of the normally secreted protein inve
rtase has in fusion constructs previously been found to reside in the
propeptide of proteinase A. We found that sorting of such a hybrid pro
tein is dependent on the vacuolar protein sorting receptor Vps10p. Thi
s was unexpected, as strains disrupted for VPS10 sort more than 85% of
the proteinase A to the vacuole. Consistent with a role for Vps10p in
sorting of proteinase A, we found that 1) overproduction of Vps10p su
ppressed the missorting phenotype associated with overproduction of pr
oteinase A, 2) overproduction of proteinase A induced missorting of ca
rboxypeptidase Y, 3) vacuolar sorting of proteinase A in a Delta vps10
strain was readily saturated by modest overproduction of proteinase A
, and 4) Vps10p and proteinase A interact directly and specifically as
shown by chemical cross-linking. Interestingly, overexpression of two
telomere-linked VPS10 homologues, VTH1 and VTH2 suppressed the missor
ting phenotypes of a Delta vps10 strain. However, disruption of the VT
H1 and VTH2 genes did not affect the sorting of proteinase A. We concl
ude that proteinase A utilizes at least two mechanisms for sorting, a
Vps10p-dependent path and a Vth1p/Vth2p/Vps10p-independent path.