Abstract
We have determined the DNA sequence for the 5' end of the arg3 gene of Saccharomyces cerevisiae, including part of the coding region and the 200 nucleotides immediately upstream. A promoter-deletion mutant was found to have lost all of the sequence lying normally in front of the gene except for the 33 nucleotides preceding the AUG codon. The role of the 5' domain in initiation and regulation of arg3 transcription was assessed by a gene fusion experiment. The Escherichia coli lacZ gene, was truncated of the eight amino-terminal codons substituted in vitro, on a 2mu plasmid, for the carboxy-terminal and 3'-flanking regions of arg3, leaving only the first 19 proximal codons and approximately 1600 nucleotides of the region preceding arg3 on the yeast chromosome. The fused gene was expressed in phase and was still submitted to the two mechanisms regulating the wild-type arg3 gene: the general, probably transcriptional control of amino acid biosynthesis and the specific, apparently post-transcriptional control mediated by the products of the argR genes. These results suggest a determining role for the 5' end portion of the arg3 messenger in the specific arginine-mediated control mechanism.