A purified, isolated polynucleotide (I) that contains a DNA sequence encoding the human glucose transporter protein, GLUT4Val85Met (II), is new. Independent claims are also included for the following: (1) Saccharomyces cerevisiae cell in which all glucose transporters are no longer functional and no functional Erg4 protein is present； (2) method for preparing yeast cells that contain (I)； (3) yeast cells in which all glucose transporters are no longer functional and which contain (I)； (4) method for identifying compounds (A) that stimulate activity of GLUT4 protein； and (5) methods for identifying compounds (B) or (C) that inhibit the proteins encoded by the Fgy1 and ERG4 genes, respectively.
