HUMAN VIRUS PROTEIN, POLIOVIRUS PROTEIN 2BC, INDUCES MEMBRANE PROLIFERATION AND BLOCKS THE EXOCYTIC PATHWAY IN THE YEAST SACCHAROMYCES-CEREVISIAE

Inducible synthesis of poliovirus, protein 2BC in Saccharomyces cerevi siae arrests cell growth in the G(2) phase of the cell cycle, while no effects are observed upon expression of poliovirus genes 2B or 2C, ei ther individually or in combination, Expression of 2BC induces a numbe r of morphological modifications in yeast cells, one of the most strik ing being the proliferation of small membranous vesicles that fill mos t of the cytoplasm, These vesicles are morphologically similar to the cytopathic vacuoles that proliferate during the infection of human cel ls by poliovirus. The transport and processing of several yeast protei ns, including vacuolar carboxypeptidase Y, aminopeptidase I or yeast a lpha-mating factor, is hampered upon expression of poliovirus 2BC, sug gesting that transport of proteins through the Golgi apparatus is impa ired by this viral protein, Finally, a number of 2BC variants were gen erated and the effects of their expression on yeast growth, cellular m orphology and protein processing were analyzed, 2BC variants defective in the NTPase activity were still able to interfere with yeast growth and the exocytic system, while deletion of 30 amino acids at the N-te rminus of 2BC impairs its function, These findings lend support to the idea that 2BC, but not 2B or 2C, is the protein responsible for vesic le proliferation in poliovirus-infected cells, In addition, the activi ty of a human virus protein in yeast cells opens new avenues to invest igate the exact location at which poliovirus 2BC interferes with the v esicular system and to test the action of other animal virus proteins potentially involved in modifying the vesicular system in mammalian ce lls.