5' untranslated sequences are required for the translational control of a yeast regulatory gene

In yeast, many genes encoding amino acid biosynthetic enzymes are subject to a common regulatory system called the general control of amino acid biosynthesis. The product of the regulatory gene GCN4 is required for an increase in transcription of general control-regulated genes when yeast are grown under amino acid-starvation conditions. In this report, we show that the expression of the GCN4 gene is regulated at the translational level: the efficiency of translation of the GCN4 mRNA is dramatically increased during growth under amino acid-starvation conditions. The complete nucleotide sequence of the GCN4 gene, presented here, reveals the existence of an unusually long 5' untranslated region in the corresponding mRNA. In vivo analysis of the effects of a deletion in this 5' leader has enabled us to define a region required for the translational regulation of the GCN4 mRNA.