Expression of the 180-kD ribosome receptor induces membrane proliferation and increased secretory activity in yeast

Expression of the canine 180-kD ribosome receptor (p180) in yeast cells res ulted in a marked proliferation of intracellular membranes. The type of mem branes observed varied with the expression of specific portions of p180, Ro ugh membranes predominated when the ribosome binding domain of p180 was pre sent, whereas expression constructs lacking this region resulted in smooth membranes, Northern analysis indicated that expression of the NH2-terminal 767 amino acids (Delta CT), which include the ribosome binding domain, upre gulated the transcription and translation of genes involved in exocytosis. The membranes that were proliferated were functional as these cells overcam e a temperature-sensitive translocation defect. Most significantly, cells t hat overexpressed Delta CT and proliferated rough endoplasmic reticulum exh ibited severalfold higher levels of secretion of an ectopically expressed s ecretory protein. We conclude that p180 expression triggers a cascade of ev ents leading to an increase in secretory potential akin to the terminal dif ferentiation of mammalian secretory cells and tissues.