Membrane protein retention in the yeast Golgi apparatus: dipeptidyl aminopeptidase A is retained by a cytoplasmic signal containing aromatic residues

It is possible that, in addition to a retrieval system, a static mode of retention may also exist wherein the static system would simply reduce the rate at which DPAP A escapes the Golgi. The static system might also recognize features of the cytoplasmic tail of DPAP A distinct from the retention signal containing aromatic residues. This model might explain why the kinetics of vacuolar delivery of mutant forms of A-ALP lacking the aromatic residue signal is somewhat slower (55 min for F87A-A-ALP) than the processing half time of A-ALP lacking most of its cytoplasmic domain (25 min for A2-100-A-ALP; Nothwehr, S., and T. Stevens, unpublished data) and that of wild-type ALP (5 min; Klionsky and Emr, 1989) . In any event, it is clear that the aromatic residue signal is an important determinant for yeast Golgi retention and further work will be needed to identify other elements within the DPAP A cytoplasmic domain, if any, that influence retention.