Molecular determinants of Golgi retention in the Punta Toro virus G1 protein

The G1 glycoprotein of Punta Toro virus, a member of the bunyavirus family, accumulates in the Golgi complex when it is expressed from cloned cDNA. We previously reported that the information necessary for Golgi retention of the G1 protein is located within the transmembrane domain and a portion of the cytoplasmic domain adjacent to the transmembrane domain (Matsuoka, Y., Chen, S.-Y., and Compans, R. W. (1994) J. Biol. Chem. 269, 22565-22573). To determine the features of the amino acid sequence motif required for Golgi retention, we have introduced mutations including truncations and point mutations in the transmembrane and the cytoplasmic domains and examined the cellular localization of the expressed mutant proteins. The results from truncation mutants indicate that the crucial information appears to be located within the first 10 amino acids of the cytoplasmic domain. Within this region, mutation of a proline residue yielded a protein that was transported to the cell surface. A protein was also expressed on the cell surface when one of the threonine residues in the transmembrane domain was changed to leucine. Thus the transmembrane domain may have a supportive role in Golgi retention, possibly by promoting protein interactions through hydroxylated side chains.