31 Yeast GCN4 Transcriptional Activator Protein

Abstract

OVERVIEW
Yeast cells respond to conditions of amino acid starvation by synthesizing GCN4, a protein that binds to the promoters of many amino acid biosynthetic genes and coordinately activates their transcription. GCN4 belongs to the AP-1 transcription factor family, which is highly conserved throughout the eukaryotic kingdom and includes the Jun and Fos oncoproteins. In this review, I discuss the following topics: the GCN4 recognition sequence and its relationship to ATF/CREB sites; the leucine zipper and basic region subdomains that respectively mediate dimerization and specific DNA-binding; the acidic transcriptional activation domain; evidence for functional interactions between GCN4 and TFIID; GCN4 activation in the absence of a TATA element; and potential mechanisms for synergistic activation.

INTRODUCTION
Yeast cells respond to starvation for any single amino acid by coordinately activating at least 40 genes from a wide variety of amino acid biosynthetic pathways (for review, see Hinnebusch 1988). This coordinate induction is mediated by GCN4, a protein that binds specifically to the promoters of the amino acid biosynthetic genes (Hope and Struhl 1985; Arndt and Fink 1986). GCN4 is synthesized only when cells are starved for amino acids, thus explaining why the amino acid biosynthetic genes are transcriptionally induced during starvation conditions (Fig. 1) (Hinnebusch 1984; Thireos et al. 1984). Moreover, the response to starvation is unlikely to involve a regulated modification of GCN4 or interaction with a coregulatory molecule, because GCN4 is a fully functional transcription factor when artificially expressed under normal growth conditions. The general control of amino acid biosynthetic...