Cell surface expression and orientation in membranes of the 44-amino-acid SH protein of simian virus 5.

Antiserum was raised against a synthetic peptide containing the N-terminal hydrophilic domain of the small hydrophobic protein (SH) of simian virus 5 (SV5) and used to characterize properties of the SH protein. SH demonstrated properties of an integral membrane protein. Indirect immunofluorescence experiments showed that the protein is involved in the exocytotic pathway, and isolation of plasma membranes from SV5-infected cells showed an enrichment of SH, indicating that SH is transported to the infected-cell surface. Biochemical analysis of the orientation of SH in membranes by proteolysis of intact SV5-infected cell surfaces and intracellular microsomal vesicles indicated that SH is oriented in membranes with its N-terminal hydrophilic domain exposed on the cytoplasmic face of the plasma membrane and the C terminus of approximately five amino acid residues exposed at the cell surface. These data are discussed with respect to positive-acting signals being necessary in the ectodomain of SH for cell surface expression.