Nucleotide Sequence of Yeast LEU2 Shows 5'-noncoding Region Has Sequences Cognate to Leucine

The LEU2 structural gene and its regulatory sequences were isolated on a 2200 bp Xho I-Sal I fragment. Sequencing of the 5'-noncoding region showed that at -151 there is an open reading frame of 23 codons of which six are for leucine. The leucine codon usage in this reading frame follows exactly that of other yeast genes. At the carboxy-terminal end and immediately after the peptide reading frame, a 14 bp hairpin (followed by a T-rich segment) can form in the putative mRNA; this arrangement closely resembles an RNA polymerase terminator. These and other features suggest a model for regulation. Preceding this is a gene (which starts at -463) for tRNALeu3, the major tRNALeu isoacceptor. RNA polymerase III transcription start and termination signals flank 5' and 3' ends, respectively, of the structural gene. The features noted above are in the same DNA strand that codes for the LEU2 gene product.