Expression of the human adenovirus E1a product in yeast

We synthesized the 13S mRNA-encoded protein of the early region 1a (E1a) of human adenovirus in Saccharomyces cerevisiae under the control of the yeast GAL7 gene promoter. Similar to the case in HeLa cells, the E1a protein in yeast was phosphorylated and formed multiple bands on sodium dodecylsulfate-polyacrylamide gel electrophoresis. These bands migrated more slowly than expected from the Mr calculated on the basis of the nucleotide sequence of the gene. Synthesis of the E1a protein caused induction of a specific family of heat-shock proteins (Hsp70), which, however, did not confer heat resistance to the yeast. In addition, the E1a production resulted in an elongation of the generation time of yeast from 2.4 h to 3.9 h, which was attributed specifically to elongation of the G1 interval in the cell cycle. In the light of these findings, we suggest that the E1a protein synthesized in yeast exerts a specific function.