2 DISTINCT YEAST TRANSCRIPTIONAL ACTIVATORS REQUIRE THE FUNCTION OF THE GCN5 PROTEIN TO PROMOTE NORMAL LEVELS OF TRANSCRIPTION

When yeast cells are grown under conditions of amino acid limitation, transcription of amino acid biosynthetic genes is increased through the action of the GCN4 transcriptional regulator. gcn5 mutant strains exhibit poor growth under such conditions. We have established that GCN4 requires the function of GCN5 in order to promote normal levels of transcriptional activation. In addition, we have shown that GCN5 is also required for the activity of the HAP2-HAP3-HAP4 transcriptional activation complex, which mediates the transcription of genes involved in respiratory functions. Thus, GCN5 is a new member of the recently revealed general class of transcriptional regulators that collaborate with certain specific DNA binding activators to promote high levels of transcription. We have cloned and sequenced the GCN5 gene. The deduced GCN5 protein contains a region conserved in other yeast, Drosophila and human proteins, all members of this new class of transcriptional activators.