Abstract
A family of secretory or transmembrane proteins have a unique glycopeptide which contains abundant, clustered threonine and serine residues. Such a sequence is also found in a yeast extracellular glucoamylase encoded by STA1. To investigate the role of the threonine- and serine-rich tract (TS) in protein secretion, I constructed and introduced into yeast a series of internal deletions of STA1 and chimeric genes which code for various amounts of Sta1 amino-terminal peptide and a constant carboxy-terminal peptide of either intracellular glucoamylase (encoded by SGA) or β-glactosidase (encoded by laeZ), and examined the secretory nature of their gene products. I found that the mutant Sta1 proteins without TS were not secreted and that the hybrid β-galactosidase proteins carrying TS were transported to the cell envelope. These results suggest that TS can serve as a signal for intracellular transport of proteins.
