TARGETING OF A HETEROLOGOUS PROTEIN TO THE CELL-WALL OF SACCHAROMYCES-CEREVISIAE

The sexual adhesion protein of Saccharomyces cerevisiae MATalpha cells , alpha-agglutinin, could not be extracted from the cell wall with hot sodium dodecyl sulfate (SDS), but became soluble after digestion of t he cell wall with laminarinase. This indicates that it is intimately a ssociated with cell wall glucan. A fusion protein was constructed cons isting of the signal sequence of yeast invertase, guar alpha-galactosi dase, and the C-terminal half of the alpha-agglutinin. Most of the fus ion protein was incorporated in the cell wall. A small amount could be extracted with SDS, but most of it could only be extracted with lamin arinase. On the other hand, cells containing a construct consisting of the signal sequence of invertase and alpha-galactosidase released mos t of the alpha-galactosidase into the medium and all cell wall-associa ted alpha-galactosidase was released by SDS. Labelling with antibodies showed that the alpha-galactosidase part of the fusion protein was ex posed on the surface of the cell wall. The results demonstrate that th e C-terminal half of the alpha-agglutinin contains the information nee ded to incorporate a protein into the cell wall.